Spinal intervertebral implant, interconnections for such implant and processes for making

ABSTRACT

A cortical bone implant is formed of two or more planks of bone which are connected with one or more offset pins. The pins may be right circular cylinders inserted into a corresponding offset bore which offset bends the inserted pin. The bending creates compression and tensile loads in the pin which loads creates friction compression forces on the planks connecting them to the pins by friction. The pins may have different shapes to form offset configurations in place of the offset bores for friction attachment to the planks. The implants may be formed of flat or L-shaped planks or bones formed into other shapes including interlocking arrangements. Processes and fixtures are disclosed for forming the pins, planks and implants. Various embodiments of the pins, planks, implants and processes are disclosed.

This application is a divisional of application Ser. No. 10/005,238filed Dec. 5, 2001 which is incorporated by reference herein in itsentirety.

This invention relates to spinal intervertebral fusion implants,processes for making such implants and interconnecting arrangements forattaching bone implants formed from planks of bone.

CROSS REFERENCE TO RELATED APPLICATIONS

Of interest are commonly owned U.S. Pat. No. 6,123,731 to Boyce et al.and U.S. Pat. No. 5,899,939 to Boyce et al. and copending applicationSer. No. 09/705,377 entitled Spinal Intervertebral Implant filed Nov. 3,2000 corresponding to PCT/US01/45551 filed Nov. 2, 2001, Ser. No.09/328,242 entitled Ramp Shaped Intervertebral Implant filed Jun. 8,1999 in the name of John W. Boyle, now U.S. Pat. No. 6,277,149, Ser. No.60/246,297 entitled Spinal Intervertebral Insertion Tool filed Nov. 7,2000 in the name of Erik Martz et al. and corresponding to PCTapplication PCT/US01/44414, filed Nov. 6, 2001, Serial No. 996243entitled Osteoimplant, Method of Making Same and Use of the Osteoimplantfor the Treatment of Bone Defects filed Nov. 28, 2001 in the name ofJohn Winterbottom et al., now U.S. Pat. No. 6,478,825 and Ser. No.60/264,601 entitled Implant Insertion Tool filed Jan. 26, 2001 in thename of John M. Winterbottom et al. and corresponding to PCT applicationPCT/US01/44414 filed Nov. 6, 2001, all incorporated by reference herein.

U.S. Pat. No. 5,899,939 to Boyce et al. discloses a bone-derived implantmade up of one or more layers of fully demineralized or partiallydemineralized cortical bone and optionally one or more layers of someother material. An adhesive, or other bonding techniques or mechanicalfasteners such as pins, screws, dowels and so on or interengagingfeatures may be used to connect the layers. The implants can be shapedby machining or press molding.

Surgical procedures using spinal implants for fusing adjacent vertebraeto treat various pathologies are well known. Implants for suchprocedures take a wide variety of shapes, forms and materials from boneto titanium inert materials, rigid and elastic, circular cylindrical,wedge shapes, cages with or without openings to accept bone fusionpromoting material. The implants are dimensioned and shaped to provide apredetermined disc space between the fused adjacent vertebra.

Generally, bone growth promoting material is used in conjunction withthe implant especially inert implants of metal, ceramic or othersynthetic compositions. Often this growth promoting material is in theform of bone chips or bone fibers. The bone source may be the iliaccrest of the patient which is not desirable due to pain and longrecovery periods.

Implants of generally one kind of design are described in certain of theaforementioned copending applications.

Published PCT international applications WO 99/09914 and WO 00/24327also disclose spinal intervertebral implants of different shapes and areincorporated by reference herein. Manufacturing processes and tools forinsertion are also disclosed.

U.S. Pat. No. 4,878,915 to Brantigan illustrates a spinal intervertebralimplant. The implant is circular cylindrical and has a threaded bore andtwo opposing radial slots at one end for receiving an insertion toolthreaded stud and prongs.

U.S. Pat. No 4,904,261 to Dove et al. illustrates an inert C-shapedspinal fusion implant.

U.S. Pat. No. 5,192,327 to Brantigan discloses a prosthetic implant forvertebrae.

U.S. Pat. No. 5,443,514 discloses a method for fusing adjacent vertebraeusing a spinal implant. The implant has through openings to provide forblood flow and bone growth from one side of the implant to the otherside of the implant to adjacent vertebra. The implant is made of choppedfiber reinforced molded polymer, stainless steel or titanium.

U.S. Pat. No. 5,522,899 to Michlelson discloses spinal implants whichare substantially hollow rectangular configurations. In one embodiment,a series of implants are placed side by side in the interverabral spaceto substantially fill the disc space. Autogenous bone material is packedwithin the hollow portion to promote bone growth. In other embodiments asubstantially rectangular member has a series of ridges on upper andlower surfaces. The material of the implants is not described.

U.S. Pat. No. 5,769,897 to Harle discloses a wedge implant having afirst component of a synthetic bone material such as a bioceramicmaterial and a second component of a synthetic bone material such as abioceramic material or bone tissue or containing bone tissue incombination with other biointegration enhancing components. The secondmaterial is incorporated in accessible voids such as open cells, pores,bore, holes and/or of the first component. The first component forms aframe or matrix for the second component. The first component impartsstrength to the second component. The first and second components canreceive one or more pharmaceutical substances. The second component canfully or partially disintegrate upon completion of the implanting topromote penetration of freshly grown bone tissue into the firstcomponent.

U.S. Pat. No. 5,716,416 to Lin discloses an elastic intervertebralimplant.

U.S. Pat. No. 5,741,253 to Michelson, discloses an implant that istubular and cylindrical and is inserted in an opening in the spineformed by a drill.

U.S. Pat. No. 5,443,514 to Steffee discloses a spinal implant that iswedge shaped with two opposing flat parallel surfaces and two inclinedsurfaces which converge toward one end. The flat surfaces have recesseswhich receive the clamp of an insertion instrument.

U.S. Pat. No. 6,200,347 to Anderson et al. discloses a composite bonegraft for implantation in a patient. The graft includes two or more boneportions and one or more biocompatible connectors which hold the boneportions together. Textured surfaces are provided. Disclosed aredifferent embodiments and shapes.

U.S. Pat. No. 6,025,538 to Yaccarino discloses a composite allograftbone device comprising a first bone member body defining a face thatincludes a plurality of intersecting grooves cut into the face defininga plurality of spaced projections of a first pattern. A second bonemember body has a face that includes a plurality of angularly spacedgrooves forming projections in a second pattern on the first bone memberbody. The projections and grooves mate to form the composite body. Anangled through bore is in the two bodies and includes a dowel mounted inthe bore.

PCT application WO 99/09914 discloses a cortical bone cervicalSmith-Robinson fusion Implant. Disclosed are different spinal implantsof cortical bone and methodology for making. The implants are D-shapedor C-shaped and may be formed in layers which are pinned together. Acancellous plug or plug made of other biocompatible material with bonegrowth materials is used with the D-shaped implant.

Fred H. Albee in Bone graft Surgery in Disease, Injury and Deformity, D.Appleton-Century Company, NY., 1940, pages 20-22, discloses thefabrication of bone pegs and screws using a bone mill and in ScientificAmerican, April 1936, Vol. No. 4, pages 178-181, discloses the formationof various bone configurations in a manner similar to woodworkingmethodology using similar tools as in woodworking. FIG. 3 thereofdiscloses various bone configurations fabricated in the mannerdisclosed. FIG. 4 shows a bone mill using various tools.

The present invention is a recognition of a need for improvements to theabove described implants and related connecting structures as well asprocessing methodology for formation of such implants.

A spinal fusion implant for fusing together two adjacent vertebraaccording to an aspect of the present invention comprises a first memberhaving first and second opposing sides and a first bore defining acentral, longitudinal first axis, the first bore being in communicationwith at least the first side. A second member has third and fourthopposing sides and a second bore in communication with at least thethird side, the second bore defining a second central longitudinal axis,the first and second axes forming a first pair. An elongated first pinis located in the first and second bores for securing the first memberto the second member at the interface formed by the facing first andthird respective sides, the pin having a first section defining a thirdcentral longitudinal axis and a second section defining a fourth centrallongitudinal axis, the third and fourth axes forming a second pair.

One axis of at least one of the first and second pair of axes is offsetrelative to the other axis of the at least one pair of axes so as toplace the pin in relative compression and tension in the first andsecond bores for providing a compressive load on the surface of thefirst and second bores to frictionally secure the members together. Thefirst and second members define a planar interface, further including aninterengaging arrangement coupled to the first and second membersadjacent to said interface for precluding translation displacement ofthe members transverse to said first and second axes in response to thecompression load on the surface of the bores.

The first member has a planar interface surface at the first side, thesecond member having a planar interface surface at the third side forabutting the first member planar surface in a plane, the first memberdefining an edge, the second member having a leg extending therefrom,the leg for abutment with the edge to form said interengagingarrangement to preclude relative translation of the first and secondmembers in at least one direction in the plane, the compression andtension creating compression forces in said members in the at least onedirection. Each member is L-shaped with the leg of each member forming arecess with its planar interface surface, each member having a portionadjacent to its leg in the recess of the other member.

A spinal fusion implant according to a further aspect for fusingtogether two adjacent vertebra comprises a first member having first andsecond opposing sides and a first bore defining a central longitudinalfirst axis, the first bore being in communication with at least thefirst side. A second member has third and fourth opposing sides and asecond bore in communication with at least the third side, the secondbore defining a second central longitudinal axis, the first and secondaxes forming a first pair. An elongated first pin located in the firstand second bores for securing the first member to the second member atthe interface formed by the facing first and third respective sides, thepin having a first section defining a third central longitudinal axisand a second section defining a fourth central longitudinal axis, thethird and fourth axes forming a second pair. One axis of at least one ofthe first and second pair of axes is offset relative to the other axisof the at least one pair of axes so as to place the pin in relativecompression and tension in the first and second bores for providing acompressive load on the surface of the first and second bores tofrictionally secure the members together; wherein the offset is formedby the at least one axis being non-parallel to said other axis.

In a further aspect, the one and other axes intersect.

A spinal fusion implant for fusing together two adjacent vertebraaccording to a still further aspect comprises a first member havingfirst and second opposing sides and a first bore defining a centrallongitudinal first axis, the first bore being in communication with atleast the first side. A second member has third and fourth opposingsides and a second bore in communication with at least the third side,the second bore defining a second central longitudinal axis, the firstand second axes forming a first pair. An elongated first pin is locatedin the first and second bores for securing the first member to thesecond member at the interface formed by the facing first and thirdrespective sides, the pin having a first section defining a thirdcentral longitudinal axis and a second section defining a fourth centrallongitudinal axis, the third and fourth axes forming a second pair. Oneaxis of at least one of the first and second pair of axes is offsetrelative to the other axis of the at least one pair of axes so as toplace the pin in relative compression and tension in the first andsecond bores for providing a compressive load on the surface of thefirst and second bores to frictionally secure the members together;wherein the first and second sections are curved forming said secondpair of axes as a single continuous curved axis.

In a further aspect, the projection of the first and second elongatedbores in a direction normal to said planes forms an X shaped image ofsaid first and second elongated bores in a plane parallel to saidparallel planes.

In a further aspect, there are two sets of said first and second boresand a second pin, the first pin engaged with the first set of bores andthe second pin engaged with the second set of bores. Each set of boresare inclined at an angle not perpendicular to the plane of the interfaceof the members, the angle of one set of bores being oriented opposite tothe orientation of the other set of bores.

In a still further aspect, the members each comprise sheet material, thesheet material having opposing surfaces defining said sides, the membersforming a wedge having proximal and distal ends, the proximal endforming an anterior end and the distal end forming a posterior end, theimplant having a longitudinal axis normal to the interface of saidmembers and extending through said proximal and distal ends normal tothe interface of said members, the elongated first pin extending alongsaid longitudinal axis.

In a further aspect, a pair of first and second pins, a different pinbeing in each member bore for attaching the members to each other, thepins and bores being arranged to place the pins in both compression andtension, at least one of the bores having first and second sections eachdefining a first transverse dimension defining a corresponding pair offirst and second respective central longitudinal axes. One axis of oneof the pair of first and second axes being offset relative to the otheraxis of the pair of axes so as to form a first offset arrangement of agiven orientation and to place the first pin in relative compression andtension in the at least one bore for providing a compressive load on thesurface of the at least one bore to frictionally secure the memberstogether.

A method of forming a bone implant according to an aspect of the presentinvention comprises assembling two cortical bone planks in parallelabutting relation, boring at least one first bore in one of the boneplanks in a first direction, and boring at least one second bore in theother of the bone planks in a second direction generally opposite thefirst direction wherein the first and second bores are offset relativeto each an amount such that a straight bone pin inserted in the bores isplaced in compression and tension.

A method of forming an implant according to a further aspect comprisesforming first and second cortical bone members with a bore in eachmember, contracting a cortical bone pin by dehydrating the pin,inserting the dehydrated pin in the bore of each member; and thenexpanding the inserted pin to create an interference fit between the pinand bone members in the bores.

A process for forming a bone implant according to a further aspectcomprises forming a plurality of planks of cortical bone, the plankshaving a broad surface terminating at edges, the surface being definedby a length and a width, the planks each having a thickness, forming thebroad surface of each of at least two of said planks for mating inabutting relation, surface demineralizing all surfaces of the at leasttwo planks, clamping together the two at least planks with said matingbroad surfaces abutting, washing the clamped at least two planks,forming at least one bore in the at least two clamped plankstransversely the broad surfaces for receiving a locking pin therein,forming a locking pin and inserting the locking pin in said at least onebore in each of the at least two clamped planks, forming a plurality ofridges on first and second opposing sides of said clamped planks,surface demineralizing the formed ridges, freezing and/or drying underclamping pressure the resulting demineralized implant; and thenunclamping the implant.

A process of making a spinal implant according to a further aspectcomprises forming first and second hydrated cortical bone planks withaligned bores, surface demineralizing a bone pin and then dehydratingthe pin, inserting the dehydrated pin into the aligned bores; and thenswelling the demineralized pin surface to provide a friction fit betweenthe pin and bores.

IN THE DRAWINGS

FIG. 1 is an isometric view of a spinal implant according to one aspectof the present invention;

FIG. 2 is a sectional plan view of the implant of FIG. 3 taken alonglines 2-2;

FIG. 3 is a side elevation sectional view of the implant of FIG. 1;

FIG. 4 is an exploded sectional plan view similar to the view of FIG. 2with the locking pins prior to insertion;

FIG. 4 a is a side elevation view of a locking pin useful for explainingcertain principles of the present invention;

FIG. 5 is an sectional plan view similar to the view of FIG. 4 of animplant according to a second embodiment of the present invention;

FIG. 6 is a sectional elevation view of the implant of FIG. 7 takenalong lines 6-6;

FIG. 7 is an side elevation view of an implant according to a thirdembodiment of the present invention;

FIG. 8 is a plan sectional view of an implant according to a furtherembodiment of the present invention;

FIGS. 9 and 10 are side elevation views of an embodiment of locking pinsused in the embodiment of FIG. 8;

FIG. 11 is a plan sectional view of an implant according to a furtherembodiment of the present invention;

FIG. 12 is a plan sectional exploded view of an implant of a furtherembodiment of the present invention;

FIGS. 13 and 15 are side elevation views of locking pins according tofurther embodiments;

FIG. 14 is a top plan view of the pins of FIGS. 13 and 15;

FIG. 16 is a more detailed view of a portion of the pins of FIGS. 13 and15;

FIGS. 17-21 and 4041 are respective side elevation views of locking pinsaccording to further embodiments of the present invention;

FIGS. 22-26 b, 27, 31 and 33 are isometric views of locking pinsaccording to still further embodiments;

FIGS. 26 c and 26 d are respective isometric views of two of the pins ofFIG. 26 b interlocked and as employed with a multiple layered implantfor securing the layers of the implant together;

FIGS. 26 e-26 f are an isometric view of crossed pins and a moredetailed cross section view of the crossed pins, respectively;

FIGS. 28 and 29 are plan views of locking pins of still furtherembodiments;

FIG. 30 is an isometric view of the pin of FIG. 13;

FIG. 32 is a plan view of a bore in an implant according to a furtherembodiment for receiving a locking pin;

FIGS. 34 and 36 are isometric views of implants according to furtherembodiments of the present invention;

FIG. 35 is a plan sectional view of an implant according to a furtherembodiment;

FIGS. 37 and 38 are respective top plan views of the implants of FIGS.34 and 36;

FIG. 39 is a plan sectional view of an implant according to a furtherembodiment;

FIGS. 42-49, 52 and 53 are respective isometric views of implantsaccording to further embodiments;

FIGS. 50 and 51 are respective top plan and side elevation views of theimplant of FIG. 49;

FIG. 54 is a side elevation view of the implant of FIG. 53;

FIG. 55 is an isometric diagrammatic view of a long bone illustratingthe fabrication of implants according to various embodiments herein;

FIGS. 56-58 illustrate in isometric views various sequential steps infabricating the implant of FIG. 59;

FIG. 59 illustrates an implant element which may be further processed toform the implants or portions thereof of FIGS. 42 and 43;

FIG. 60 illustrates an isometric view of a long bone used to fabricatethe implant portion of FIG. 59 and bone planks used to form implantsaccording to the various disclosed embodiments;

FIG. 61 is an isometric view of one of the bone planks of FIG. 60 afterfurther processing;

FIGS. 62-65 and 67 are sectional plan views of different embodiments ofimplants according to the present invention;

FIG. 66 is an exploded view of an implant and locking pin according toan embodiment of the present invention using the pin of FIG. 23;

FIGS. 68-70 are respective isometric, side elevation sectional and topplan views of a tool for fabricating several of the disclosed lockingpins;

FIGS. 70 a-70 d are plan views of further embodiments of the tool ofFIGS. 68-70;

FIG. 71 is a side elevation view of an implant with a locking pin in abore thereof for securing several bone planks together;

FIG. 72 is a side elevation sectional view of an implant according to afurther embodiment useful for explaining certain principles of thepresent invention;

FIG. 73 is an isometric view of an implant with a groove cutting tool;

FIG. 74 is an isometric view of the implant of FIG. 73 after the groovesare formed in a surface thereof;

FIGS. 75-77 are isometric views of implants according to furtherembodiments;

FIG. 77 a is a sectional side elevation view of the implant of FIG. 77;

FIG. 78 is an exploded view of a stack of planks for forming an implantaccording to a further embodiment;

FIGS. 79-82 are isometric views of a cortical bone plank useful forexplaining certain principles;

FIG. 83 is a side elevation view of a tool useful for creating certainbores in a representative embodiment of an implant;

FIG. 84 is an isometric exploded view of a tool for processing animplant according to certain of the disclosed embodiments;

FIGS. 85 and 86 are side elevation sectional views of a tool forinserting pins into the bores in an implant;

FIG. 87 is an isometric view of a tool useful for shaving a portion offof an end of an implant;

FIGS. 88 and 89 are plan views of different portions of the tool of FIG.87;

FIG. 90 is an isometric view of an implant according to a furtherembodiment;

FIGS. 91 and 92 are isometric views of the identical pieces forming theimplant of FIG. 90;

FIG. 93 is a representative side elevation view of one of the pieces ofFIGS. 91 and 92;

FIGS. 94 a and 94 b are isometric views of implants of furtherembodiments;

FIG. 95 is an isometric view of a cortical bone ring partially processedfor forming the implant of FIGS. 97 and 98;

FIG. 96 is an exploded side isometric view of the bone pieces formedfrom the ring of FIG. 95 prior to assembly;

FIGS. 97 and 98 are respective top plan and side elevation views of animplant formed by the pieces of FIG. 96;

FIG. 99 is an isometric exploded view of an implant inserter tool andbone implant for use with the inserter; and

FIG. 100 is a top plan view of the inserter and implant of FIG. 99assembled showing the temporary attachment of the inserter and implant.

The intervertebral wedge shaped implant 10, FIGS. 1-3, which is alsoreferred to as a graft, is bone derived, preferably relatively hardcortical bone, and, in a further embodiment, may be formed generally asdescribed in more detail in the aforementioned patent application Ser.No. 09/328,242 now U.S. Pat. No. 6,277,149, incorporated by referenceherein. The implant, as well as the other implant embodiments describedbelow, may also be fabricated as described in the aforementioned U.S.Pat. No. 5,899,939 incorporated by reference herein in its entirety. Theimplant 10 has a top surface 12, a bottom surface 14, two opposite endsurfaces 16 and 18 and two opposing side surface 17 and 19. The surfaces12 and 14 have ridges or saw teeth 20. The teeth 20 are formed byparallel grooves normal to the longitudinal axis 22 of the implant andextend completely across the surfaces 12 and 14. The teeth 20 have aninclined rake 24 facing end 18 and a rake 26 facing end 16. Rake 26 isnormal to the axis 22 so that the teeth 20 bite into the vertebra topreclude migrating out of the disc space after insertion. The implant isinserted anterior end 18 first, which is higher dimension h than theposterior end 16. Thus the rake of the teeth preclude the implant frommigrating out of the disc space opposite to the insertion direction. Theangle of inclination of rake 24 may be about 45°. The grooves formingthe teeth may be about 1 mm in depth for an implant having thedimensions set forth in the aforementioned copending application Ser.No. 09/328,242. These teeth form serrations in the form of repetitiveidentical saw teeth. The saw teeth have a pitch which is determined fora given implant configuration. The rake surfaces may be both inclinedrelative to the implant longitudinal axis 22. The teeth 43 serve toprevent withdrawal of the implant after insertion.

Surfaces 12 and 14 are preferably inclined to form a wedge shapedimplant, sometimes referred as a ramp, but also may be rectangular ofuniform thickness or curved as in a cylindrical dowel. Surfaces 12 and14 of implant 10 converge at posterior end 16, to a height in the rangeof about 7 to 13 mm. The height increases toward the respective anteriorend in the range of about 9 to 15 mm in one embodiment. Other shapes andconfigurations are described below herein in reference to others of thefigures.

Surface 16 is planar and forms the posterior end and surface 18, whichis formed rounded with two radii R, FIG. 1, and which forms the anteriorend of the implant. Surfaces 12 and 14 each have a tapered or chamferedportion 28 at end 18 to facilitate insertion of the implant into a discspace to minimize trauma to the patient.

Preferably the implant is formed from cadaveric human or animal bonean/or bone composites of sufficient strength comparable to cortical boneto support adjacent vertebra when fused thereto, and more preferably ofa long human or animal bone and comprising primarily cortical bone,which is hard and exhibits relatively good strength.

The implant 10 comprises two sheets or planks 30 and 32 of corticalbone. The term sheets as used herein and in the claims is intended toinclude planks, wafers and other relatively thin sheet-like material andas used herein is interchangeable with such other terms. Sheet materialof different thicknesses and according to the relative shape arereferred to as planks herein in the interest of illustration of arelatively long sheet with a narrower transverse dimension as commonwith conventional material known as planks. Preferably, the sheets orplanks forming the implant 10 are formed from a cortical ring cut from along bone, such as the fibula, ulna, humerus, tibia or femur by cuttingthe bone transversely across the diaphysis or metaphisis of the bone asshown in FIG. 60. This forms a cortical ring 36.

In FIG. 60, long bone 34 is typically formed from larger bones to formimplants for thoracic and lumbar spinal fusion. Smaller bones includingthe ulna, radius and fibula are used to form implants for cervicalspinal fusion. The bone 34 is cut into a ring 36 having a central opencore 38 formed by the medullary canal. The bone is cut into planks 40which are elongated rectangular sections with opposing planar sides andparallel edges. An L-shaped member 42 may also be cut from the bone toform an implant structure as described later. The planks 40 are furtherprocessed to form a finished plank. The cut bone is secured and theedges machined to provide, in one embodiment, a substantiallyrectangular plank with squared edges as shown by implant plank 44, FIG.61.

In the alternative, the planks may be formed as followed. In FIGS.87-89, a clamp assembly 170 clamps a bone 158, cut from a donor longbone, to form end 171 into a plank. Clamp 170 comprises a base 172having a rib 174. Rib 174 slides in guide slot 176 (FIG. 89) of a sawtable 175. The base 172 has a rectangular recess 178 for receiving acomplementary shaped clamp 180. Clamp 180 has a rectangular body 182.Body 182 has a flange section 184 overlying section 186 of the base 172.Alignment apertures 188 are used to align clamp 180 to the base 172alignment apertures 190. Alignment pin 192 is inserted in apertures 188and 190 to align the clamp 180 to the base 172 at the desired position.

A clamp bar 194 is screwed to body 184 by screws 164 to clamp the bone158 to the clamp 180. The clamp 180 is secured by screw 181 to base 172.This clamp 170 forms a fixture that permits incremental cutting of thebone 158 into planks with 0.5 mm increments depending upon the holecombination of apertures 188 and 190 set by pin 192. The clamped bone158 when attached to the base 172 permits the overhanging end 171 to besliced by saw blade 196 of table 175. The bone may be adjusted inposition by resetting the pin 192 in different apertures in the clamp.Employing this technique bone planks may be formed. This arrangementallows easy adjustment of the clamp 180 position relative to the sawblade 196. Large easily seen markings (not shown) on the clampcomponents and the large pin 192 permits ease of adjustment. The claim170 is precisely positioned in the slide slot 176 which aligns the clamp170 and clamp 180 via the slide rib 174 in the slot 176. Once the clampscrew 181 is tightened, the clamp 180 is positioned against the wall 183of the base 180 forming recess 178. This prevents angular displacementof the clamp 180 and provides accurate alignment of the clamp 180 to theblade 196. The above techniques are given by way of example. Other knownfabrication techniques may be used to accurately machine the implantbody to the desired dimensions.

The planks 40 may be in a range of less than 1 mm to in excess of 20 mmthick. Preferably the planks 30 and 32, FIG. 1, of implant 10 have athickness 46 of about 10-20 mm each to form a composite two plankthickness 48 of about 20-40 mm. The planks have a length defined by ends16 and 18 of about 20-30 mm and preferably 23-26 mm. The anterior end 18height h of the implant 10 may be about 7-18 mm and preferably 9-15 mm.The posterior end 16 may have a height of about 5-15 mm and preferablyabout 7-13 mm. The width may be about 7.8 to 8.8 mm. The opposing sides12, 14 of the implant in contact with adjacent vertebrae in theposterior to anterior direction, as determined by the site of theimplant in the patient, may taper at an angle of about 5 degrees. Thesedimensions are formed in the implant 10 after the planks are attached toeach other.

In FIG. 2, two planks 30 and 32 which may be identical, may also bebonded together at their broad surfaces which mate in complementaryfashion. Such bonding is disclosed in U.S. Pat. No. 5,899,939 discussedin the introductory portion. In the present embodiment the broadsurfaces are planar, but in other embodiments these mating surfaces mayhave interlocking surface features such as projections and grooves,e.g., dove tail joints and mortise and tendon joints and the like asdescribed below in more detail. Preferably the mating surfaces arepartially demineralized to assist in bonding these surfaces together. Inaddition, adhesives, as described in the aforementioned U.S. Pat. No.5,899,939 patent may be preferably employed.

Prior art approaches to securing multiple planks together relied ondifferent diameters between locking pins and the bores in the planks inwhich the pins are inserted. This difference in diameters is employed tocreate an interference fit between a locking pin and the plank bores.For example, U.S. Pat. Nos. 6,200,347 and 6,025,538 disclose for examplepress or interference fit of pins into mating bores in the graft formedof multiple layers. The disadvantage of this approach is that when theimplant is dried, the hole size relative to the pin may lead tosplitting of the bone planks as shown in FIGS. 80 and 82. In addition,the planks may become loose and may no longer be affixed by the pins.When the interference is reduced to prevent splitting, the holding powerof the pins is reduced. Thus the interference arrangement isunsatisfactory.

In FIG. 80, a plank 138 is shown with its fibers 139 running indirections 140. If two pins 142 were inserted into corresponding boresin the plank 138 in interference fit, the compressive and shear loadsfrom the pins would cooperate reinforcing each other to cause the plankto split at splits 144 which tend to separate the plank into twolongitudinal pieces. However, if the fiber directions 145 are normal tothe plank longitudinal axis 143 instead of parallel, as shown in FIG.82, the splits 145 caused by pins 146 are normal to the axis 143 and donot cooperate with splits caused by other pins. This latter action ismore preferable than that of FIG. 80 as the magnitude and tendency tosplit is reduced. Therefore, the fiber directions of the planks ispreferably normal to the longitudinal axis 22 of the implant.

Two bores 52 and 54, FIG. 4, are formed in the composite blank formed byplanks 30 and 32. The term “bore” as used herein does not imply that thebore is a through bore or that all portions of the bore are identical.In this embodiment, the bores 52 and 54 have different bore sectionswherein only a portion of the sections are in communication with eachother and other portions have stepped surfaces. Bores 52 and 54 aremirror images of each other and are oriented approximately 180° relativeto each other in the two planks 30 and 32. Bore 52 comprises a subset ofoffset bores 56 and 58 whose central axes are offset in the longitudinaldirection of the implant axis 22. Bore 54 comprises a subset of offsetbores 60 and 62 whose central axes are also offset in the longitudinaldirection of the implant axis 22. Subset bore 56 is preferably identicalto subset bore 60 in diameter and subset bore 58 is preferable identicalto subset bore 62 in diameter and, more preferably, all of the subsetbores 56, 58 60 and 62 are identical in diameter.

The subset bores 60 and 62 are offset distance 64 and the subset bores56 and 58 are also offset the same distance 64. Bore 60 has an axis 66and bore 62 has an axis 68 with the axes offset from each other bydistance 64. Similarly, the axes of subset bores 56 and 58 are offsetfrom each other, but in an opposite direction as the direction of offsetof the subset bores 60 and 62.

Thus bore 60 is displaced from bore 62 in direction 70 of the implantlongitudinal axis 22 and bore 56 is axially displaced on axis 22 frombore 58 in direction 72 opposite to direction 70. Preferably the offsetdistance 64 is about 0.1 to 1 mm for a bore 52 or bore 54 diameter of3-5 mm, the subset bores each being circular cylindrical. This offsetrange value may differ in accordance with a given implementation and thestrength and fiber characteristics of the particular bone being used.Thus the offset distance 64 of each of the respective bores 56 and 60 inplate 30 is in a direction toward each other relative to the axes of thecorresponding subset bores 58 and 62. This relative direction of theoffset is important.

In FIG. 83, the bores 52 and 54 are formed by tool 74. Tool 74 comprisesan upper tool steel guide 76 and a lower tool steel guide 78. The guides76 and 78 include locating pins (not shown) for aligning guide holes 80,82, 84, and 86 relative to each other to produce the bores 52 and 54.The guides 76 and 78 are clamped together by a clamp not shown in thisfigure.

Guide holes 80 and 82 receive drill bit 88 of a drill for drilling therespective bores 56 and 58 and the guide holes serve to guide the bit 88to form respective bores 60 and 62. The tool 74 may be used to formbores in the various implant embodiments described hereinafter withminor modifications to accept the different implant and boreconfigurations. This arrangement provides precision bore locations inthe implant. The tapered tip of the drill bit chamfers the edge of thebores in the adjacent planks. This chamfering permits ease of passage ofan offset pin from one bore to the other in the adjacent planks. Afterdrilling the bores, the pins can be pressed into place withoutdisturbing the clamped guides 76 and 78.

In FIG. 4, a right circular cylindrical bone pin 90 by way of exampleand which could also be tapered is inserted into each bore 52 and 54.The pin 90 has a diameter that is substantially the same as that of thebores 52 and 54 so that there is no press or interference fit betweenthe pin and bores. The pin 90 is cortical bone and its fibers 92 rungenerally along the pin longitudinal axis 94. This direction of thefibers gives the pin 90 maximum shear strength in the transversedirection to resist shearing of different sections of the pin in thepresence of shear forces medially the pin along its axis 94 due to theoffset of the subset bores in which it is inserted. The pin 90preferably by way of example may have a diameter in the range of about 2to 5 mm according to the dimensions of the implant involved and thecorresponding bore sizes. Other diameters of the pins may be usedaccording to a given implementation.

A pin 90 is forced into each bore 54 and 52. In FIG. 85, planks 30 and32 are clamped between two dies 96 and 98. A plunger 100 on tool 102mates in a corresponding bore of the die 96 and is forced in direction104 against the pin 90 by an operator mechanism (not shown) such as athreaded or hydraulic drive. The pin 90 is then forced into the subsetof bores 56 and 58 of respective planks 30 and 32. The pin 90 endsurfaces, when the pin is fully inserted, are flush and coextensive withthe outer side surfaces of the implant comprising the two joined planks30 and 32.

In FIG. 86, the pin 90 is shown fully inserted. After insertion, thetool 102 is used to insert a second pin 90 (not shown) into the otherbore 54 similarly via tool guide hole 106.

In FIG. 4 a, pin 90 is a right circular cylinder and has two opposingend surfaces 91 and 93 which are flat and normal to the longitudinalaxis 94. As mentioned the cortical bone fibers have a directiongenerally parallel to the axis 94. The end surfaces 91 and 93 afterinsertion of the pin 90 into the bore 52 or bore 54 are flush with thesides of the 17 and 19 of the implant 10 as also mentioned above. Asshown in the figure the pins 90 appear bent. However, in practice thisbending is exaggerated as the offset value 64, FIG. 4, is relativelysmall.

When the pin 90 is forced into the bore 52 or 54, it bends somewhat inresponse to the offset axes of the bore sections 60, 62 or 56, 58 of thetwo bores 52 and 54. The bend occurs generally at the interface betweenthe two planks 30 and 32 at which the offset between the two bores isfirst reached by the pin upon insertion. In FIG. 4 a, the pin 90 is thusbent as manifested in principle by the dashed lines 106 and 108 whichare shown merely for purposes of illustration as the pin in practice isbent as shown in FIG. 2.

The bending of the pin 90 creates both latent compression and tensileforces in the pin as known from general strength of materials principlesrelating to bent beams. If the pin 90 is assumed to be bent in thedirection of the dashed lines 106 and 108 for purposes of discussion,then the region of the pin to the left of the axis 94 in the figure willbe in compression as shown by arrows 110. The region to the right of theaxis 94 will be in tension as shown by arrows 112. The compression andtension create latent compressive and tensile potential energy resilientforces in the pin and also place the pin in shear. These forces act in adirection to straighten the pin to its original configuration as shownin FIGS. 4, 4 a and 17.

In respect of pin fabrication, bones are anisotropic, i.e., strengthvaries according to direction due to the fibrous structure. To maximizepin strength, the fiber direction is in the axial length direction ofthe pin. In this way transverse shearing forces must break the fibers,FIGS. 79 and 81. If the force is in the direction of the fibers, thefibers can separate as shown in FIGS. 80, 82. The pins may be made ofbone such as the ulna and radii or left over scraps from bone used tomake the implant planks.

The larger the pin diameter, the greater its holding power. The surfacearea of a pin increases with its diameter, i.e., A=πd L where A is thesurface area, d is the diameter and L is the length of the pin. Thusdoubling the pin diameter also doubles the surface area. Since in theoffset pin arrangements, the compression loads induced on the adjacentimplant surfaces is utilized to create static friction forces, thegreater the surface area the greater the friction load for a givenforce. Therefore, the pins should be as great a diameter as possible fora given implant configuration. This can be determined empirically foreach implant design.

Hole saws are preferable for generating pins, Pins using such saws werefabricated with diameters as small as 1.5 mm. Hand held saws as well asmachine operated saws may be used according to the saw design. Sincebone is relatively elastic, extremely high precision in making the pinsis not required. In such cases, once the pins are formed no othermachining of the exterior outer surface is required other than cuttingthe pins to length. In contrast, metal pins require a much greaterdegree of accuracy to obtain a given fit in a bore. Centerless grindingmay be used to increase pin diameter tolerances. Such a process isespecially useful for fabricating tapered pins. Because of theelasticity of bone, obtaining a friction fit can be achieved withoutextremely tight tolerances.

Pin bores are formed by drills which are available in all desired sizesand will complement the various pin diameters formed by hole saws. Suchbores may also be finished with reamers if desired. Pins made of boneare axially strong in compression. However, the pins are relatively weakin bending and in radial expansion. These deficiencies can be overcomeby inserting the pins through tubes or holes that provide radial supportto the pins so that the pins can not expand radially outwardly underinsertion loads, FIGS. 85 and 86. The guide holes should be longer thanthe pins and the pins are driven by closely matched plungers such asplunger 100. The plunger has a shoulder to limit the depth of insertioncontacting the surface above the guide hole such as surface 107, FIGS.85 and 86. The pin insertion depth may be any desired value with the pinflush or recessed into the implant bore or extending somewhat above theimplant surface.

In general bone has spring back. This means the ID of a hole is slightlysmaller than the corresponding drill size. The bone pins might fiteasily into the drill guides but manifest a tight press fit in the boredholes. The bore size can be determined empirically by one of ordinaryskill in this art according to various pin sizes being used, the textureand hardness of the pins and relative pin diameters and pinconfigurations. A drill guide may have a flared out top to allow easybone pin insertion and a taper near the bottom to reduce the guidediameter to precisely the diameter of the hole in the implant.

Tapered pins which mate with tapered bores with shallow angles, e.g.,less than about 10 degrees, are self locking. Forming a tapered bore issimple using a custom drill or reamer. A tapered pin is formed after thecylindrical pin is formed. Pins may be left unfinished after formationor may be sanded or ground to provide a smooth exterior to integrate thepin surface with the implant bore surface.

In FIG. 2, pin 90 on the left hand side of the implant generates acompressive force component in direction 114 in plank 30 and an equalcompressive force component in direction 116 in plank 32, which forcesare components of the latent compressive and tensile bending forces ofthe pin in the direction of the plane of the plank normal to the pinaxis. These forces lock the planks 30 and 32 in their abutting relationprecluding their separation. However, these forces do not tend to splitthe planks at the bores since the compressive forces are applied by thepin in only one direction in each plank. In contrast, an interferencefit applies forces at the bore in opposite directions in the plank.These opposing forces tend to split the plank at the bore as discussedabove. In the offset arrangement there are no opposing forces on theplank which would tend to separate the plank in the fiber direction atthe bore.

Normally, without other restraining structure, the forces in directions114 and 116 would merely slide the planks 30 and 32 relative to eachother in these directions until the pin 90 is straight. Thus, arestraint is necessary to oppose the thrust from the misalignedbores-pins. This is to keep the planks in place resisting the opposingthrust forces in these directions. This restraint can take the form of anumber of different embodiments. The basic construction principle ofmisaligned bores is effective no matter the orientation of the pins,parallel or angled to each other. The advantage is that holding powercan be satisfactory with little or no diametrical interference betweenthe pin and hole which greatly reduces the chances of splitting theplanks.

In the present embodiment of FIG. 2, the above described restraint is inthe form of a second pin 90 in the right hand side of the implant 10drawing figure. This second pin 90 is inserted into offset bores 56, 58(FIG. 4) which are offset to the same degree as bores 60 and 62 but inopposite directions to the offset of bores 60 and 62. That is, theoffset of bore 58 relative to bore 56 is to the right in the drawingfigure, direction 70, whereas the offset of bore 62 relative to the bore60 is to the left, direction 72. Consequently the pin 90 in bore 52 isbent the same amount as the pin 90 in bore 54 but in the oppositedirection along axis 22 (FIG. 3). Therefore, the compression forces inthe planks 30 and 32 created by the right hand pin 90 are equal andopposite in directions 114 and 116, FIG. 2, to the directions of theforces created by the left hand pin 90. The forces of the two pins thuscounteract each other and prevent the planks from moving in the axialdirection, directions 70 and 72, FIG. 4. The resulting compressive loadson the planks 30 and 32 by the two pins frictionally locks the pins tothe planks and thus locks the two planks together in a direction normalto the axis 22.

The pin fibers have a fiber direction generally normal to axis 22 andpresent a maximum resistance to shearing of the pins by the shearingforces in directions 114 and 116. These shearing forces are created bythe compression loads on the planks at the offset plane. By offsettingthe bores receiving both pins 90, a maximum locking action of the twoplanks in a direction normal to axis 22 is provided. It should beunderstood that the two planks are by way of example and any number ofpins may lock together any number of planks as described herein.However, both pins need not be bent or inserted in offset bores. Onlyone such pin need be bent and the other pin may be inserted in astraight through bore (not shown in this embodiment) and held in placeby a typical interference fit and/or bonding, for example. The other pinmay be held in place by such friction interference fit, an adhesive orother securing arrangements.

This other pin prevents the axial displacement of the planks along theimplant longitudinal axis 22 (FIG. 2). Still other arrangements may beprovided to preclude relative axial displacement of the two planks 30and 32 in response to the opposing compressive loads presented by one ormore bent pins 90 in a corresponding offset bore.

In the alternative, friction fit of pins may be obtained by swelling ofbone from hydration. This process requires the cutting of the pins anddehydrating them. The dehydration may use any process such as a vacuum,air drying and/or freeze drying, or any other desirable process. Thedried pins are placed in normal (hydrated bone) bone, then the pinnedimplant is immersed in saline to hydrate and swell the pins. Thereafter,the pins will match the hydration state of the mating bone and thefriction load should remain through freezing, freeze drying, rehydrationand so on of the pinned implant. Rehydration of the pins can crack thesurrounding bone if care is not taken. Therefore, relative dimensions ofthe pin and bores need be carefully matched. Once the pin is attached inthis way, variations in the environment including temperature andhumidity will affect the pins and implant uniformly so that bothcontract and expand in unison retaining the friction fit.

Another consideration in maximizing the strength of the implant 10 is tooptimize the strength of the planks 30 and 32 in the presence of thecompressive forces presented by the bent pins 90. In FIG. 79, a plank118 has fibers 120 which have a fiber direction 122. If a shearing force124 is presented normal to the fiber direction 122, the fiber portions126 will merely bend in the direction of the force 124 rather thanshear, as shown. In FIG. 81, however, in plank 128, the fibers 130 runin directions 132. In this situation, a shearing force 134 will separatethe plank portion 136, separating it at the location of the shear force134. Therefore, shearing forces where applicable are created normal tothe fiber direction when possible.

Thus while two offset pins-mating bores are shown in FIG. 2, only one ofsuch pins-bores needs to be so offset. The two offset pins-bores ofcourse provide additional holding power to hold the two planks togetherand is preferred.

The implant 10 side walls 17 and 19 and top and bottom surfaces 12 and14 are machined to form configurations such as the preferred taper,radii and saw teeth ridges of the implant 10, or left in their naturalperipheral configuration (not shown). Other shapes as disclosed laterherein may also be provided as desired. The angle of the wedge surfaces12 and 14, FIG. 3, are arranged to accommodate the inclination of theadjacent vertebra to maintain the natural curvature of the spine. Thevarious dimensions of the implant are disclosed in the aforementionedcopending applications and patents incorporated by reference herein.

Surface demineralization reduces surface hardness and so can reduceprecision needed in pin and hole machining. A problem is that the grainof the bone runs parallel to the axis of the pin and thus demineralizedsurface layers on the pin can be sheared off relatively easily, FIG. 81.Another problem is that the flexibility of demineralized surfaces meansthat micromovement of bone layers relative to one another under load canonly be poorly constrained by demineralized pins. This leads to lowerfatigue strength for the implant assembly. The more the demineralizedlayer on the pins is compressed, the more effective as a loadtransmitting surface. A practical way of achieving surface compressionis to insert dehydrated, surface demineralized pins into a hydratedbone.

When the pin is dried after surface demineralization, it will shrinksignificanty, and especially at the demineralized layer. The dry pin canbe inserted as a loose press fit such that the demineralized layer isnot damaged by the insertion. Upon rehydration, the demineralized layerwill swell, providing a tight fit in the bone planks. Any other use ofdemineralized pins is not preferred. Thus inserting dry pins with alight press fit results in the demineralized layer not being sheared offduring the insertion of the pins.

Instead of or in conjunction with such surface demineralization of thepins, the bores in the implant receiving the pins can also be surfacedemineralized. Demineralization generally weakens the bone fibers. Whenthe fibers in the bores run perpendicular to the bores, there is lesspossibility of shearing of the demineralized surface in the bores thanon the pins. Furthermore, by demineralizing the bores, the load bearingdiameter of the pins will not be reduced as might occur when the pinsare surface demineralized. Therefore, it is preferable to use surfacedemineralized bores with undemineralized pins. However, surfacedemineralized pins may be used with surface demineralized mating boresif desired.

The planks with surface demineralized bores preferably have the boresformed somewhat undersized with respect to the pins so that the surfacedemineralized layers will be compressed upon pin insertion. Drying theplanks before pin insertion after the bores are formed is not preferredbecause this leads to shrinkage of the bore diameters. Thus, the pinsmay be inserted after their being dried to provide the desired fit, butmay be inserted without such drying.

To surface demineralize the bores in the planks, the entire plank issurface demineralized after the plank bores are formed. The planks maybe demineralized while assembled in the bore forming fixture such asillustrated in FIGS. 83 and 84. Reference is made to commonly owned USPats. Nos. 5,899,939, 6,123,731, 5,314,476, 5,507,813 and 5,298,254 foradditional processes for making bone implants and related structures andincorporated by reference herein.

The planks may also be secured by adhesives with or without pins, screwsor other mechanical fastening arrangements including interlockingprojections and recesses and so on. Bone may be treated to make itadhesive without the use of an additional adhesive substance. See theaforementioned U.S. Pat. No. 5,899,939. Such treatment can includepreparing a deminerlized collagen layer adhesive or recrystallizing thedeminerlized surfaces to form interlocking crystals. Adhesives as aseparate substance can also be employed.

In collagen bonding, the surfaces to be bonded are demineralized. Acombination of heat and pressure produces the desired bond of theabutting demineralized surfaces. The exact mechanism for such bonds isnot understood, but such bonds appear to be relatively weak. It isbelieved that strength may be imparted to the bonded joint by adding aningredient that improves collagen solubility such as a salt. Further,the effect on inductivity by increasing collagen solubility is notknown. Also, the ability of such bonds to withstand immersion in bodyfluids is also not known. It is believed better to bond bone fiber endswith a collagen bond rather than the collagen fibers parallel to thesurface being bonded.

In recrystallization bonding, bone surfaces are painted with acid whichpromotes strong bond formation at least while the bone is dry. Such abond dissolves in the presence of saline. It is known to use calciumphosphate self setting cements. Such cements may be used for suchrecrystalliztion bonding. Such cements are stable in body fluids. In oneexample, a cement system employs hydroxylatpatite and phosphoric acid.The bone contains hydroxylapatite as its mineral base, and painting thesurfaces with phosphoric acid forms a stronger bond than when thesurfaces are painted with hydrochloric acid, forming a calcium phosphatecement.

Recrystallization bonding may be used to strengthen the implant ofmultiple bone planks for insertion into the disc space, for example,when the implant planks are not rehydrated. This provides an advantageover collagen bonding in that there is little or no demineralized layerpresent at the bond once the recrystallization effect dissipates. Thusthe implant will exhibit greater strength than one with an internalcollagen bond layer.

Recrystalliztion can be carried out by soaking or painting the bonesurfaces with any acid, phosphoric acid being preferred. The wetsurfaces are then joined. Bonding is enhanced by pressing the surfacestogether under pressure and then drying the implant under pressure. Thebonding process can also be used to bond a pin to an implant in theimplant bore.

Total demineralization of one or more pin segments may also be useful.These segments are flexible due to the demineralization and may stretchunder tensile load. During insertion, the pins are pulled in place sothe demineralized segment stretches and, in response, shrinks indiameter. After insertion, the tensile force is removed, the pin relaxesand the demineralized segment returns to its normal configurationincreasing in diameter locking the pin in place in interference fit withthe mating bore.

Acid for adhesion of bone elements whether pins to the planks or planksto each other can be applied after assembly and delivered to thecontacting surfaces by capillary action. Therefore, the acid need not beapplied prior to assembly to obtain an adhesive bond.

In a variation of the acid treatment process described above, the boneplanks can be assembled into an implant, and the assembled implant isthen subjected to an acid treatment as discussed. The acid diffusesbetween the contacting bone surfaces. This effects the required amountof dissolution especially if the clamping pressure is minimized whilethe diffusion is in process. This process may be used in conjunctionwith the disclosed processes in the aforementioned U.S. Pat. No.6,123,731 incorporated by reference herein.

If the implant with multiple planks is dried rather than stored frozen,warpage can be a problem. Normally implants made from bone do not warpor change dimensions when frozen. The warpage can cause cracks to appearbetween the bone planks. To resolve this problem, different approachesmay be used individually or in combination. These approaches includeminimizing the shrinkage, or constraining the implant so that warpagedoes not occur, or causing the planks to adhere so they cannot separate.

By removing most of the moisture by drying the implant at a temperatureabove freezing reduces shrinkage significantly, compared to freezedrying where the implant is frozen during most of the water removalprocess. After drying the implant at a temperature above freezing,remaining residual moisture may be removed by conventionalfreeze-drying, without introducing any additional shrinkage. In thealternative, glycerol may be introduced into the bone to reduceshrinkage prior to freezing and may also be used to assist in swellingthe implant.

Physical restraint by clamping the implant during drying reduces thetendency to warp. Physical restraint is also beneficial in retaining thedimensions of the implant. For example, a threaded pilot hole for aninsertion instrument can shrink during drying to the point where it isdifficult or impossible for the inserter threads to engage the implant.A rigid screw placed in the hole before drying minimizes this problem.

The efficacy of the adhesion process can be enhanced if the boneassembly is clamped together and dried above freezing before a freezedrying step is carried out. The clamp can be retained or removed duringa subsequent freeze dry cycle but retention is preferred.

To optimize support of spinal loads on the implant, it is preferred thatthe implant bone fibers run parallel to the spinal column. This is shownby the fibers 50, FIG. 1. However, since the spinal bone in contact withthe implant is relatively softer, this fiber orientation may not benecessary and it may be advantageous to have the fibers parallel to thevertebra to optimize the strength of the implant during insertion intothe disc space. In this regard, it is preferred that the planks beformed from the bone in the length direction of the bone, FIG. 60. Inthis way the fibers will run along the length dimension of the implantin the implant insertion direction. However, the problem with this fiberorientation is that if the load bearing surfaces are demineralized,there is the chance the demineralized surface might be scraped off ofthe implant during insertion due to its weakness. See FIGS. 79 and 81 inthis regard.

The process for forming the implant such as implant 10 is as follows.The implant is formed from planks formed from a long bone as describedin connection with FIGS. 60 and 61. The planks are then cut to thedesired length and width of the implant, e.g., 0.5 to 20 mm thick. Thevarious surfaces of the planks are then machined as applicable to formthe plank 44, FIG. 61. The planks are then partially surfaceddemineralized by dipping into a 0.6 normal HCL solution for apredetermined time period corresponding to the desired depth ofdemineralization. Only the outer surface portions of the bone will bedemineralized. The strength imparting interior portions of the plankswill not be compromised. Moreover, the bone may be treated using avariety of bone healing enhancing technologies. For example, bone growthfactors may be infused into the natural porosity of the bone and/or thebone may be infused with acid to further demineralize the internalmatrix of the bone where desired. These treatments may be performedusing the pressure flow system disclosed in U.S. Pat. No. 5,846,484incorporated by reference herein. While human bones are preferred,non-human animal bones may also be used.

The two planks 30 and 32 are then pressed together by a clamp asillustrated in FIGS. 83-86. In FIG. 84, planks 30 and 32 are placedbetween two clamp dies 96 and 98. The planks are placed in recess 148formed by raised L-shaped portion 150 of the die 96 as best seen in FIG.86. The die 96 abuts the portion 150 and stud 152. Two screws 154, 156clamp the planks between the dies, FIG. 86. The bores in the planks arethen formed as explained in respect of FIG. 83. In FIG. 83, the guides76 and 78 represent the clamp dies 96 and 98, FIG. 84-86. The pins 90are then formed and surface demineralized. The pins are formed from thelong bone with the fibers oriented as discussed above.

The planks are transferred to a further clamp (not shown) so that theserration teeth may be formed. In FIG. 73, the clamped body 158 formingthe implant is placed adjacent a rotating cutter 160 which cuts theteeth 164 into the body. As the teeth 164 are being formed the body 158is translated in direction 161 to form elongated teeth. The oppositeside 162 of the body 158 is then formed with the identical teeth 164after the teeth are formed on one side, FIG. 74. In FIG. 74 the teeth164 are different than teeth 20 to show a different configuration. Herethe teeth 164 are formed as spaced V-shaped grooves in the body surface.One side of the groove is inclined at 45 degrees to the longitudinalaxis and the other side is normal to the axis. The inclined side is onthe posterior end 166 side of the grooves and the normal side of thegrooves is on the anterior end 168 side of the grooves to provide bitinginto the mating vertebra in an implant withdrawal direction from theinserted position.

The bores 170, FIG. 74, for the locking pins are then formed in the body158 after both sides of the body 158 are grooved. The body 158 aftersuch machining is then surfaced demineralized. The surfacedemineralization of the bores is advantageous in that the fibers in thebores run perpendicular to the bore. There is thus much less chance ofshearing the demineralized surfaces in the holes than on the pins. Also,demineralization of the bores means that the load bearing diameter ofthe pins will not be reduced as might occur when the pins are surfacedemineralized. It is preferable to use surface demineralized bores withundersized pins. However, surface demineralize pins can also be usedwith surface demineralized bores.

The body is then dried under clamp pressure and removed from the clamp.This pressure is provided by the clamps. The ambient air pressure may beabove or below atmospheric pressure and is independent of the clampingpressure. The pins 90 (FIG. 1) are then inserted in the bores asdescribed above.

During surgery, anterior end 18 of the implant 10, FIG. 1, is insertedfirst between the adjacent vertebra in the posterior approach. In thisapproach normally two incisions are made on opposite sides of the spinefor corresponding separate implants. In the alternative, the posteriorend may be inserted first in an anterior approach.

In FIG. 5, an alternative implant 198 comprises planks 200 and 202formed as described in connection with implant 10. The difference isthat bores 204 and 206 are curved with radius rather than linear. Thebores 204 and 206 each are mirror images of the other. The portion ofbore 204 in plank 200 is also a mirror image of the portion in plank202. The portion of bore 206 in plank 200 is a mirror image of the boreportion in plank 202. The curves of the two bores emanate from radiiextending in opposite directions. The curvature of the bores isexaggerated for illustration and may be represented by straight boresinclined relative to each other in mirror image angles relative to theinterface of the two planks 200 and 202.

A straight pin, such as right circular cylindrical pin 90, FIG. 17, isinserted into each the bores 204 and 206 which also are circular incross section. The pins 90 when inserted into the bores 204 and 206become bent. When bent they exhibit tension and compression as discussedabove. The tensile and compressive beam loads form compression loads onthe planks and frictionally hold the planks together. These loads aresimilar to the loads discussed in connection with pin 90, FIGS. 4 and 4a.

FIGS. 6 and 7 illustrate a further embodiment of a locking borearrangement. Implant 208 comprises two planks 210 and 212 of corticalbone as described for the implant of FIG. 1. The difference is theorientation and position of the bores for receiving the locking pins 90.The implant 208 has two bores 210 and 212. Bore 210 is oriented at about45° relative to the plane of the interface between the planks 214 and216 forming the implant. Bore 212 is oriented at the same angle but inthe opposite direction as shown. Bore 212 is positioned medially betweenthe longitudinal axis 218 of the implant 208 and side 220. Bore 210 ispositioned medially between axis 218 and the side 222 opposite side 220.Both bores extend generally in the longitudinal direction of axis 218 asbest seen in FIG. 7. The bores 210 and 212 in each plank have offsetsections forming offset subsets of bores similarly as the bores ofimplant 10, FIG. 4. The bore section 210′ of bore 210 in plank 214 isoffset distance 224 from bore section 210″ in plank 216. Similarly, thesections of the bore 212 in planks 214 and 216 are offset the samedistance 224′ as distance 224.

A straight pin similar to pin 90, but longer is inserted in each of thebores 210 and 212. These pins are each placed in tension and compressionin response to their bending in a manner as described for pin 90discussed above. The tension and compression loads of the pins transferto the planks as axial compression load components in the direction ofthe implant longitudinal axis, frictionally holding the planks together.The bores 210 and 212 being in opposite orientation, restrain axialslippage of the planks in response to the pin compression loads whichare exerted in opposing directions on the two planks. Thus the bendingof the pin 90 as described in connection with FIG. 4 a occurs also inthe bores 214 and 216. The pins in the two bores 210 and 212 thuscooperate to hold the planks connected. In FIG. 6, note that the bore210 forms a first elongated bore and the bore 212 forms a secondelongated bore. The first and second elongated bores lie in spacedparallel planes as seen in FIG. 7. The projection of the first elongatedbore 210 and the second elongated bore 212 in a direction normal to theplanes (as depicted in FIG. 6) form an X shaped image of the twoelongated bores in a plane parallel to the parallel planes (and to thedrawing sheet).

In FIG. 8, implant 226 comprises two like mirror image planks 228 and230 except for the bores therein. The planks 228 and 230 comprisecortical bone prepared as described above for the FIG. 1 embodiment. Thedifference is bores 232, 234, 236 and 238. Bores 232 and 234 form anoffset subset identical to respective offset subset bores 236 and 238and are oriented in mirror image relation along the longitudinal axis240 of the implant. Bores 232, 234, 236 and 238 are all circularcylindrical and of the same diameter. Bores 234 and 238 are normal tothe axis 240. Bore 232 is at angle α and bore 236 is at angle β to theaxis 240 which angles are preferably the same value but oriented inopposite directions. In this case the offset is created by the differentangles of the subset of bores forming a common bore.

A straight right circular cylindrical pin 243, FIGS. 9, 10 and 22, isinserted in offset subset bores 236 and 238 which are aligned at theinterface of the planks 228 and 230. A second pin 243′ identical to pin243 is inserted in aligned offset subset bores 232 and 234. The pin 243in response to the relative different angular orientations of the bores236 and 238 is bent as shown in phantom in FIG. 9. Similarly pin 243′ isbent as shown in phantom in FIG. 10. The bending of these pins createstension and compression forces in each pin which create compressionloads in the implant longitudinal axial directions of the arrowsassociated with the pins of FIGS. 9 and 10. These compression loads holdthe planks 228 and 230 together due to the friction between the pins andthe planks. The different angular orientation of the aligned bores inthe planks 228 and 230 thus form an offset relationship of the boressimilar to the offsets described in the embodiments above in the sensethe offsets create equivalent compressive and tensile forces in theassociated pins.

In FIGS. 13, 14 and 30, in the alternative, pin 242 is used in multipleplank implants having a pin receiving bore (not shown) which is astraight through bore of a common diameter with no offset subsetsections as in the above embodiments. Pin 242 has two sections 244 and246. These sections are identical in diameter and are each rightcircular cylinders of cortical bone whose fibers run along the lengthdirection as described for pin 90. Section 244 has a centrallongitudinal axis 244′ and section 246 has a central longitudinal axis246′. The axes are offset from each other a distance 248. The sections244 and 246 are separated by a shoulder 247 which is planar and normalto the axes 244′ and 246′.

When the pin 242 is inserted in a straight cylindrical bore, thesections 244 and 246 tend to bend in a direction normal to their axescreating compressive and tensile forces in the pin in similar fashion asthe forces created in pin 90, FIG. 4 a. These compressive and tensileforces create compressive forces in the mating planks which are heldtogether as a result of the static friction loads between the pin andplanks created by the plank compressive forces.

In a further alternative, pin 250, FIG. 15, has two offset rightcircular cylindrical sections 252 and 254. These sections are alsooffset a distance such as the distance 248 of pin 242, FIG. 13. Pin 250sections 252 and 254 are not separated by a planar shoulder such asshoulder 247 between the sections 244 and 246 of pin 242. Instead, thesections 252 and 254 are interconnected by inclined section 256. Section256 is circular in transverse section. Section 256 has an axial extentsufficient to provide a taper between the sections 252 and 254 whichprovides a gradual interface between the sections and which permits thepin 250 to be easily inserted in a straight bore of one diameter.

For example, in FIG. 12, two identical pins 250, 250′ are inserted incorresponding identical bores 258, 258′ in implant 260 which isotherwise identical to implant 10, FIG. 1. FIG. 16 shows the interfaceregion between the two sections 244 and 246 of pin 242, FIG. 13 in moredetail. The dashed line shows the interface region of the sections 256,258 and 254 of the embodiment of FIG. 15. The pins of both embodimentsof FIGS. 13 and 15, when inserted in the bores 258 and 258′ of FIG. 12,bend and create the compression and tensile loads in the pins which lockthe pins to the planks of the implant 260.

In FIG. 11, implant 262 comprises three cortical bone planks 263, 264and 265 prepared similarly as the planks of implant 10 except for thebores. The implant includes a third central plank 264 whose posteriorend is flat whereas the posterior end of the planks 263 and 265 arecurved with radii as shown in the figure. The implant has two bores 266and 268. The bore 266 is identical to the bore 268 except it is inmirror image relation in the implant and are longitudinally axiallyspaced from each other. Each bore 266 and 268 is in three sections. Eachsection is in a corresponding plank 263, 264 or 265. The bore sectionsare each identical in diameter but are offset as shown. The boresections in exterior plank 263 are axially aligned with the boresections in exterior plank 265 in a direction normal to the longitudinalimplant axis. The bore sections in interior plank 264 are offset axiallyin the longitudinal direction of the implant from the bore sections inthe exterior planks. The amount of offset is as described above for theimplant of FIG. 4. The offsets of the bore sections in interior plank264 are displaced in opposite directions relative to each other in thelongitudinal implant direction.

Right circular cylindrical pins 270 and 270′ of cortical bone arefabricated to about the same dimensions, preferably as close indimensions as possible, it being recognized that it is difficult tofabricate bone elements as identically as metal components. The pins 270and 270′ are inserted into corresponding bores 266 and 268 whichpreferably are the same, but in practice may differ in dimensions due tothe fact the bores are formed in bone. These pins are bent by the offsetrelation of the bore sections creating compressive and tensile loads inthe pins which transfers into compressive loads on each of the planks.These loads hold the planks together.

In FIG. 21, cortical bone pin 270 is similar to pin 242, FIG. 30 exceptit has a cap 272 at one end. The pin 270 has two offset pin sections 274and 276 which are offset similarly as pin 242. The cap 272 is discshaped and may be recessed in a countersunk bore (not shown) in themating implant. The cap assists in preventing the pin from migratingthrough the mating implant bore in at least one direction.

In FIG. 23, pin 278 is cortical bone which is formed in a curved bentconfiguration with a radius 280. This pin is preferably used with astraight right circular cylindrical bore in the mating implant plankssuch as with implant 260, FIG. 12, or may be used with offset boresections in a bore such as the bores in the implant of FIG. 4. Thecurved pin would be inserted in the offset bore with the curvatureextending in a counter direction of the offset direction of the bores toprovide increased compressive loads. Not shown are edge chamfers on thevarious pins which may be provided to facilitate insertion into thevarious bores.

FIG. 24 shows a three edged pin 282 whose edges 283 extend in the pinaxial direction as radially extending ribs. The pin 282 has parallelflat end surfaces and a curved peripheral surface between the edges 283which surface may be a circular segment or a segment of some other curvesuch as an ellipse and so on. This pin is inserted in a right circularcylindrical bore in the implant. The edges 283 lie on a diameter greaterthan that of the mating bore so as to dig into the surface of the boreto provide interference frictional fit with the bore. The externalsurface of this pin need not be demineralized or at least the edgesmasked from such demineralization.

FIGS. 25, 26 and 27 show respective square, hexagonal, and elliptical(284) in transverse cross section pins having straight longitudinalaxes. These pins are inserted in right circular cylindrical bores havinga diameter less than the largest transverse dimension of the pin so thatthe pin is in compressive interference with the body of the implant inthe bore. The corners of the square and hexagonal pins dig into themating bore surface of the implant. The elliptical pin 284 is shown indashed lines in FIG. 32 and the bore is shown in solid line. The bore iscircular cylindrical. The edges of the small radii end of the pin are incompressive interference fit with the bore surface of the implant.

Pin 271 of FIG. 26 a is fluted with the flutes running approximatelyparallel to the longitudinal axis of the pin. Pin 273 of FIG. 266 has atransverse groove or channel 275. Channel 275 is a segment of a circleor approximates such a segment. In FIG. 26 c, two pins 273 intersect ata right angle with their channels 275 interengaged, by way of example,and may intersect non-perpendicular to each other at other angles. Theseinterengaged pins thus are locked to preclude axial displacement indirections 277 and 279 relative to each other. The pins 273 can be usedto attach the layers 267 of implant 269, FIG. 26 d, together. The pins273 each optionally may be press fit into the mating bores of theimplant 269 to provide a friction interference fit. The pins are pliablebone so that they may ride over one another as they are inserted in themating bores until the channels 275 overlie each other and interlock.This interlock locks the pins to the implant. Once locked, the layers267 can not easily separate and the assembly forms a reliable unit.

In FIG. 26 e, pins 301 and 303 are assembled to an implant (not shown inthis figure) similar to the implant 269 of FIG. 26 d. The implantcomprises multiple layers which are held together by the pins 301 and303. These pins preferably have smooth surfaces such as pin 90, FIG. 17,but may have roughened surfaces as pins 304 and 308, FIGS. 19 and 20,respectively. The two pins are assembled in crossed angular relation,angle δ which may be about 60°, for example. The pins cross each otherin interference fit so that the contact region 305 may be compressedsomewhat by the compression loads imposed by the pins on each other. Thebores in the implant for these pins thus intersect to provide thisinterference during assembly.

Pin 285 of FIG. 28 is similar to the pin 282 of FIG. 24 except the edges283 of pin 282 are rounded in pin 285.

In FIG. 29, pin 286 is similar to the square pin of FIG. 25 except thecorners are rounded. The rounded corners 286′ dig into the surface ofthe mating bore of the implant to provide interference compressive fitwhich frictionally locks the implant planks together.

In FIG. 31, pin 288 comprises two sections 290 and 292 which are mirrorimages of each other. Section 290 has a longitudinal axis 293 andsection 292 has a longitudinal axis 294. The axes are inclined relativeto each other at an angle δ. This pin has sections similar to the boresof the implant 226 of FIG. 8. However, each section 290 and 292 isinclined relative to a plane 295 at the interface of the two sections.The angle δ preferably may have a value in the range of 1-10° as do thecorresponding angles of the various bores and pins described in theabove embodiments in which a section of the bore or pin is inclinedrelative to a plane parallel to the implant plank interface. This angleof inclination range is also applicable to the curved pins or bores suchas pin 278, FIG. 23 or bore 204, 206, FIG. 5 including the angles α andβ, FIG. 8. The value of the angle is a function of the pin material andits brittleness and its abililty to compress so as to distort and bendas applicable without fracturing the associate pin. The same rationaleis also applicable to the values of the offsets of the pins and bores.The pins must be able to distort and bend without fracturing undertensile and compressive loads.

Pin 296, FIG. 33, is circular cylindrical with a plurality of radiallyextending ribs 298. The ribs 298 extend for the length of the pin inthis embodiment but may be foreshortened in other embodiments byremoving the shaded material. the shaded regions on a given rib would berepeated on all of the ribs which would be identical. In thealternative, ribs comprising the shaded regions may be mixed on a givenpin as desired. The ribs have rounded edges with sides that slopeinclined toward the main pin circular body or are normal to the body atthe junction therewith.

In use, the pin 296 is inserted in an implant bore that is straight andof a diameter that is the same as the diameter of the body of the pinfrom which the ribs 298 project. In this way, the ribs are eithercompressed by the implant in the implant bore or dig somewhat into thebone of the implant in the bore to provide compressive locking of thepin to the implant planks locking the planks together.

In FIGS. 18-20, respective pins 300, 304 and 308 have correspondingrespective external threads 302, an external knurled surface 306 or aroughened external surface 310 to further assisting the pins to grip themating bore surfaces in an implant. The surface 310 may comprise aplurality of small projections and/or dimples such as may be provided bycompressing or otherwise texturing the surface with a textured materialhaving a granular surface somewhat like sandpaper. Such surfaces may beprovided to pins of the different shapes as described above wherepractical. The pin peripheral surfaces may be entirely or partiallyroughened.

In FIG. 40, pin 312 has a concave annular surface 314 and in FIG. 41 pin316 has a convex annular surface that resembles a barrel shape. In use,these pins are inserted in an implant bore that is circular cylindricalof a diameter that is the same as about the smallest diameter of thepins. In pin 312, the implant bore has a diameter of about the size ofdimension 320 and in pin 316 the mating bore has a diameter of about thesize of dimension 322.

Pins with different cross sectional geometries can be used to relievestresses as the bone planks shrink upon drying, which tends to minimizethe development of cracks in the planks. Such pins with different crosssectional areas than the mating bore in the implant are as shown in FIG.71 and can be used to obtain a friction fit. In FIG. 71 pin 410, ofsquare cross section (FIG. 25) is placed in a circular bore 412 ofimplant 413. Other pins with different shapes were discussed inconnection with FIGS. 25-29, for example, to obtain friction fits withthe mating bores. The spaces around the pins provide the desired stressrelief as the bone planks shrink to minimize the cracking of the planks.

While pins have been described made of cortical bone, the pins may bemade of other biocompatible materials such as polymers, metals and otherknown biocompatible materials. Further, the ends of the pins can bespread apart to also increase holding power. Punching the end of a pinis one way to achieve such spreading. Such swaging relationships forexample are utilized in the metal fabrication art. In addition, wedges,or smaller pins (not shown) may be employed to spread the ends of theinserted pins apart. These further pins and wedges are made of the sameor biocompatible material as the pins.

In the above embodiments, the pins and offset bores, where the termoffset includes both offset axes and angular differences in sections ofa bore receiving a pin, have closely matching diameters so that there isnegligible interference fit between any of the pins and thecorresponding bore diameter. Thus the holding power is provided withlittle or no diametrical interference between the pin and the matingbore. The tensile and compressive bending loads in the bent pin, due toeither pin bent shapes as shown in FIG. 23 or 31 or offsets of pinsection axes, creates compression loads in the mating implant bonefibers without inducing undesired splitting.

Holding power is increased by establishing an angle between the pins asshown in FIGS. 6 and 7. Angled pins have the property that they opposeseparation of the planks by virtue of their geometry. This reduces theburden of friction fitting the pins to just being able to keep the pinsfrom shifting or falling out of the respective bores. This arrangementis considerably easier to implement than holding the plates together,FIGS. 6-8, 63 and 65-67. In FIG. 63 two pins 372 and 374 are placed incorresponding bores in planks 376 and 378 of implant 380. Even withoutinterference fit, this arrangement has increased holding power for theplates. The holding power is thus significantly increased in theembodiment of FIG. 65 wherein the straight cylindrical pins 382 are inopposing offset angled bores of implant 384. In FIG. 67, implant 386 hastwo offset bores 388, 389 wherein bore 388 is generally normal to theinterface 392 between planks 390, 391 and bore 389 is at an acute angleto the interface, i.e., non-perpendicular. In FIG. 64, the three planks394, 395 and 396 of implant 397 are similar to the arrangement of theFIG. 11 implant except the bores 397, 398 thereof are arranged with theoffset sections 397′ and 398′ 180° in opposite directions from that ofthe FIG. 11 implant embodiment.

In FIGS. 68-70, a tool is shown for forming bone pins. Pins may be alsobe formed with a core saw, i.e., a circular cylindrical saw blade.However, there may be some dimensional variations among saws and thiscan lead to an unacceptable variation in pin diameters among thedifferent pins made on different saw blades. In the figures, the tool400 resolves this dimensional variation problem.

Tool 400 is a tool steel die used to finish bone pins to a finaldiameter. In FIG. 69, the die 400 has a bore 402 which terminates atsmaller diameter bore 404. Bore 404 terminates at conical bore 406 inrecess 408. In use, all pins are fabricated slightly oversize indiameter. These pins are then forced through the bores 402, 404 and 406.The smaller diameter bore 404 shaves the pins to a standard diameter ofthis bore. The larger diameter bore 402 protects the pin from spreadingby enclosing it while the pin has an axial force applied thereto.

In FIG. 70 a, a tool die 401 is similar to tool 400 except that the pinforming die bore 403 is square to form a square pin such as pin 410,FIG. 25. In FIG. 70 b, die 405 has a triangular bore 407 for forming atriangular in section bone pin. In FIG. 70 c, die 409 has a sextupletbore 411 for forming pin 415, FIG. 26. In FIG. 70 d, die 417 has an ovalbore 419 for forming pin 284, FIG. 27. Should the pins prior to forminghave a relatively large transverse cross section, then the pin may beshaped by a series of dies (not shown) having progressively smallerbores for shaving the pins to the desired shape and size gradually. Thisprogressive forming minimizes damage to the bone that might otherwiseoccur. Such progressive forming may also be applied to the correspondingbores wherein the bores may be formed relatively small in diameter andthe diameter progressively increased until the desired diameter isobtained.

Bores may be formed by broaches (not shown) which differ slightly indiameters or shaped cross sections. The final bore shape and dimensionsare thus obtained by gradual incremental formation. Alignment devicesmay be used to align the pin being formed with the die bores. Such diesmay comprise a series of stepped dies axially aligned to progressivelyform the pins or bores. The shapes of the bores and pins may also begradually changed progressively, for example, from a rectangular crosssection to circular, triangular or polygon for example, in smallincremental steps. The dies are accurately formed to form the bores andpins to precise dimensions required for a given implementation.

For deep bore cuts, a tapered broach or a series of broaches, eachslightly larger than the immediately preceding die can be used. Informing bores, first a hole is drilled of a diameter about the smallestdimension of the desired bore geometry. Then a shaped broach forms thefinal bore configuration.

In FIG. 34, implant 324 preferably comprises two cortical bone members326 and 328. Member 328 is formed from a flat plank as described abovein connection with FIGS. 60 and 61, such as plank 44 or formed asdescribed in connection with FIGS. 87-89. Member 326 is more complex andis L-shaped. Member 326 has a base portion 330 and a leg 332 whichextends at a right angle to the base portion. Leg 332 has an innersurface 334 facing the surface 335 of the base portion 330 forming arecess 336. The member 328 fits into the recess 336. The surfaces 338and 340 taper toward each other and toward the posterior end 342 to forma wedge shape. The sides 344 and 346 are parallel. the surfaces 338 and340 may also be grooved (not shown).

The L-shaped member 326 is formed as shown in FIGS. 55-59. In FIG. 55, along bone 348 of a donor is schematically represented. The bone 348 issliced into a plurality of rings 350. The fibers 352 extend in thelongitudinal direction of the long axis of the bone. The ring 350appears as shown in FIG. 56 wherein the central opening 354 is formed bythe femoral or medullary canal. In a first step, FIG. 57, the canal 354is reshaped as a rectangular opening 356. The opening 356 is formed by abroaching tool as well known in the machine tool fabrication art. InFIG. 58, two saw cuts 358 and 360 are made to form the broached ringinto two L-shaped bodies 362 and 364. The two L-shaped bodies are thenfinished into the an L-shaped member 366, FIG. 59, having a base 368 anda leg 370 extending from the base.

The member 328 may be formed from a band saw from cortical rings orcortical strips and sanded to fit into the desired shape and dimensionsto fit in the recess 336, FIG. 34.

In the implant 324, two pins 414 are inserted into corresponding boresthrough the base portion 330 and the filler plank member 328. Both boresmay be offset as shown in FIG. 2. In the alternative, in FIG. 37,implant 416 has one optional through bore 418 through the base portion420 and flat plank filler member 422 and is of constant diameter. Asecond bore 424 is offset as bore 52, FIG. 4. The offset of bore 424 issuch that the axis of bore 424′ is closer to leg 426 than bore 424″ inmember 422. This offset relationship forces the straight pin inserted inbore 424 to force the member 422 in direction 428 against the leg 426.The optional straight pin-bore combination of bore 418 may be eliminatedif desired or if used may be used with the various different shaped pinsof FIGS. 21-33 to provide enhanced gripping of the mating bone planks.

In FIG. 72, an implant 430 has an L-shaped member 432 and a flat plankfiller member 434. This implant has two offset bores 436 and 438. Bore436 has offset bores 436′ and 436″. Bore 438 has offset bores 438′ and438″. In FIG. 72, by way of example, the dimensions may be as follows:

-   -   1) C<D        ${\left. 2 \right)\quad\left( {A - B} \right)} > \frac{D - C}{2}$        Where in general D−C=about 0.2 mm for 3 mm diameter pins.

The net result is that the forces on the two pins oppose each other andlock the pins to the planks.

In the alternative, in FIG. 62, implant 442 employs an L-shaped bonemember 444 and a flat filler plank member 446. The implant may have theoverall shape of implant 324 of FIG. 34. The difference is that implant442 has a single offset bore 448 similar to bores 52 and 54, FIG. 4discussed above. The offset of subset bore 450 to subset bore 452 is indirection 454. The offset of bore 450 bends the normally straight pin indirection 454. As a result, the bend in the pin creates a compressionload in the member 446 in direction 454′. This compression load forcesthe member 446 against the leg 458 of the member 444, locking the plankmember frictionally against the leg 458, which may be roughened slightlyto increase the friction load thereon imposed by member 446. Also, theleg 458 may have an inclined surface as shown in dashed line 460 towedge the plank member 446 against the surface of base portion 462 ofmember 444. The member 446 may also have a complementary inclination atthe end surface abutting the leg 458.

The net result is that the plank 446 is forced against the leg 458 ofmember 444. Bore 436, FIG. 72, may thus be omitted to further increasethe force against the leg 458 induced by pin 414 in bore 438 since a pinin bore 436 tends to displace the plank 434 away from the leg 440.Preferably, two bores are offset in the same direction as bore 438wherein a bent pin in both bores reinforce each other in displacement ofthe plank 434 against the leg 440 holding the planks in tighterrelationship.

This implant is strong during insertion and while supporting spinalloads. Employing a single L-shaped member with a flat plank fillermember provides advantages in ease of assembly and yet provides arelatively strong implant during insertion. Assuming the wider end isthe anterior end which is inserted into the disc space first, theinsertion forces on the member 328 does not displace this memberrelative to member 326 since it abuts the member 326 leg. The two pins414 resist axial displacement of the member 326 relative to member 328during insertion due to insertion loads. Since only one member 326 mightdisplace relative to the other member 328 except for the pins, the leghelps resist insertion shear loads on the pins to preclude failureduring insertion. However, the selection of bone for the filler plankand the L-shaped member may be more critical in that the bones should bematched so that they react uniformly in response to changes in theenvironment. Bone separation due to such changes is not desirable.

In FIG. 35, in a further embodiment, implant 464 comprises two outerL-shaped members 466 and 468 and an inner third layer plank member 470which is planar. The member 470 fits closely in the recess space 472between the two outer members 466 and 468 formed by their respectivelegs 466′ and 468′.

Two pins 474 and 476 are placed in respective aligned bores in themembers 466, 468 and 470. The pins 474 and 476 are normally rightcircular cylinders of cortical bone. The corresponding bores are offsetas shown in FIG. 64 by way of example. In further alternatives, thebores may be offset and/or at angles as in FIGS. 63, 65 and 67. In afurther alternative, the pins may be bent as in FIGS. 23 and 31 or ofother shapes as shown in FIGS. 21 and 24-33. Further, the offset may bein opposite directions to the offset illustrated in FIG. 64 so that thepins are bent in opposite directions to the pins of the embodiment ofFIG. 64. The result is still opposing forces created by the two pins.This embodiment has the same advantage during insertion as theembodiment of FIG. 34. Here, the leg 466′ abuts the central member 470which abuts the leg 468′. Thus insertion loads are resisted by member468 that are exerted on the central member 470 and on member 466. Onlymember 468 might displace in response to insertion forces thereon to theleft in the figure. Such forces are resisted by the two pins 474 and476. Thus only part of the insertion load is borne by the pins.

FIG. 39 illustrates a three layer implant 478 comprising three flatplanks 480, 482 and 484. This implant is by way of example as more thanthree planks may also be used. The planks are joined by two pins 486 and488. The pins 486 and 488 are shown as circular cylindrical insertedinto offset bores. The offset is as described in connection with FIGS.35 and 64, for example. In all of the above implants, the exteriorsurfaces are formed into wedge shapes with two opposing tapered sides asin the FIG. 1 embodiment or with straight sides on all sides. Further,the implants as described above and below herein may have furthersurface features for receiving implant insertion tools as known in thisart. Such features may included threaded bores and/or slots or channelsfor receiving mating insertion tool complementary features fortemporarily securing the implant to the insertion tool. The planks ofthis implant can each displace longitudinally in response to insertionloads in case of pin failure. The two pins absorb all of the relativedifferences in insertion forces on the three planks.

In FIG. 36, a further embodiment of an implant 490 comprises two matingL-shaped cortical bone members 492 and 494. Member 492 includes a basemember 496 and a leg 498. Member 494 includes a base member 500 and aleg 502. Two cortical bone pins 504 are inserted into two mating offsetbores 506 and 508. Bore 506 comprises bore 506′ in member 496 offsetfrom bore 506″ in member 500. Bore 508 comprises bore 508′ in member 496and bore 508″ in member 500. Bores 506′ and 508′ are each offset in thesame direction of directions 510 relative to bores 506″ and 508″respectively. This same direction of the forces reinforce each other todouble the holding power of a single pin.

The legs 498 and 502 abut the base portions of the respective members496 and 500 to preclude axial displacement of the members toward eachother in directions 510. The pins 504 bend in a direction so that theleg 498 is forced against the member 500 and the member 496 is forcedagainst the leg 502 in one of directions 510 to the right in the figure.During assembly, the base portions of the various embodiments employingan L-shaped member are pressed against each other without applying aforce to the legs to provide even pressure between the base membersduring assembly.

In this embodiment, the anterior end 495 is inserted first into the discspace and the member 500 absorbs all of the insertion loads. There is noor negligible insertion load on the member 492. Therefore, there islittle shear force on the pins at the junction between the members 496and 500 as compared to the embodiment of FIG. 34.

In the embodiments of FIGS. 34 and 36, the upper and lower surfaces ofthe respective implants facing respectively toward the top and bottom ofthe drawing figure are tapered forming a wedge shape. The upper andlower surfaces may be grooved as in the embodiment of FIG. 1. Theseupper and lower surfaces abut the vertebra. The pins are horizontalrelative to the vertebra and generally parallel thereto. In this casethe insertion load is applied against the upper and lower surfaces 338and 339, FIG. 34 or surfaces 496′ and 497 in the implant 490 of FIG. 36.The edges of the members 494 and 496, FIG. 34, or the edges of themembers 494 and 496, FIG. 36, of implant 490 engage the vertebra. It ispreferable that the bone fibers run vertically between the surfaces 496′and 497 and normal to the longitudinal axes of the pins 504 to precludeshearing action as shown in FIGS. 79 and 81 during insertion. The fiberdirection then would run as shown in FIG. 82 relative to the pins. Thefact that the pins and bores are substantially the same diameterprecludes the splitting shown in FIG. 82.

In FIG. 42, in the alternative, implant 512 includes an L-shaped member514 and a plank member 516. The L-shaped member 514 has a base member518 and a leg 520 at one end of the base member. The implant has taperedsurfaces 522 and 524 which converge at posterior end 526. Surface 522includes a surface of the leg 520 and a surface of the plank member 516.These tapered surfaces as in all of the embodiments are formed after theplank members are assembled. In this embodiment, the plank member 516fits in the recess 528 formed by base member 518 and the leg 520.Therefore, the broad surfaces 522 and 524 abut the adjacent vertebrainstead of the edges as in the embodiments of FIGS. 34 and 36.

The implant 512 has two pins 530 and 532 which are in the verticalorientation relative to the vertebra when the implant is inserted. Thepins are offset and the mating bores are straight cylindrical bores asin the embodiment of FIG. 12 or the pins are straight circular cylindersand the bores are offset as in FIG. 4. In a further embodiment one pinmay be offset and one pin may be at an angle or both pins at an angle asdisclosed in the various embodiments discussed above.

Implant 534 of FIG. 43 is similar to implant 490, FIG. 36. Implant 534differs from the implant 490 by way of orientation with respect to theinsertion direction of the implant. As in the embodiment of FIG. 42, thetwo pins 536 and 538 are oriented vertically with respect to theinsertion direction so that the pins abut the adjacent vertebra. Theimplant 534 and pins are cortical bone. Either the pins are offset as inFIG. 12 or the bores are offset as in FIG. 4. In other embodiments,there may be a single pin or the pins may be at different angles as inFIGS. 63 and 67. Also, all other embodiments of pin shapes, offsets,angles and direction of offsets as discussed above are applicable tothis embodiment.

FIG. 44 illustrates implant 540 which comprises two planks 542 and 544attached by pins 546, 548. The planks are in the form of a wedge withtapered opposing surfaces 550 and 552. This implant differs from theimplant of FIG. 1 in that the gripping teeth 20 of FIG. 1 are omitted.The pins of this embodiment are offset the same as the pins of theimplant of FIG. 1. The sides of the implant may also be tapered.Further, the insertion end may be chamfered to facilitate insertion. Oneor more of the planks can be fully or partially demineralized beforeassembly in this embodiment and that of FIG. 1. A fully demineralizedplank may in some cases be encased by partially demineralized plankswhich partial demineralization should be a minimum if so used. Forexample, the central plank in FIGS. 35 and 39 may be fullydemineralized. This implant is strong for supporting spinal compressionloads and is reasonably stable under rotational loads with the advantagegoing to the implant with the fewest layers, two as compared to three,for example. This implant is easy to fabricate. However, this embodimentmay be wasteful of bone. Also, it may be weak in insertion loadresistance wherein the pins might absorb most of the insertion forces.

In FIG. 45, implant 554 comprises two planks 556 and 558 of corticalbone and two cortical bone pins 560 and 562. Here, the planks areoriented so that their broad surfaces engage the adjacent vertebrainstead of the edges as in implant 540 of FIG. 44. The pins are verticalwith respect to the vertebra orientation after insertion into the discspace. The pins are offset as described above in the variousembodiments.

In this embodiment, the planes of the planks are parallel to thevertebra and is strong in supporting compression loads exerted by thevertebra. It is expected that this implant is rotationally stable whichincreases with two members instead of three. It is easy to fabricate andwith respect to the embodiment of FIG. 44, there is less chance of layerseparation because the layers are mainly under compression rather thanshear. Bone planks formed from a long bone parallel to the bone axisfrom which they are cut are believed to be advantageous for thisembodiment as compared to the vertical oriented planks of FIG. 44.However, like the FIG. 44 embodiment, this embodiment is relatively weakduring insertion due to the shear loads on the plank members during theinsertion, which loads are absorbed by the pins.

In FIG. 46, implant 564 comprises a plurality of axial stacked planks566, 568 570 and so on generally of the same thickness, but this is notcritical. The planks 566 and so on are square or rectangular in planview in accordance with a given implementation. In this embodiment, theplanks are square. The opposing side surfaces 572 and 574 are paralleland the opposing top and bottom surfaces 576 and 578 are flat andtapered to form the implant in a wedge shape. The planks may be formedas discussed in respect of the FIG. 87 embodiment. The fibers of theplanks extend in the longitudinal direction of the pin 580. A singleaxially extending pin 580 passes through all of the planks.

The pin is preferably press fit in this embodiment as there is no secondpin provided to resist sideway slippage of the plank layers due tocompressive forces of a bent pin. Also, the various layers are alsopreferably bonded to each other to enhance the joining of the layers.The pin in the alternative may have the different shapes as discussedabove to assist in joining the planks. This orientation of the planksprovides enhanced resistance to shearing forces during insertion of theimplant in direction 582. In the alternative, two or more pins may beprovided with one or more with offsets at each plate as described above.The fiber direction of the planks may be oriented normal to theinsertion direction to provide increased resistance to insertionshearing forces.

The finished implant may have tapered upper and lower surfaces as wellas tapered sides. In addition, a chamfered end may be provided theinsertion end of the implant to facilitate insertion. In addition,surface features such as holes, threads, slots and so on can be providedfor an insertion tool (not shown). This implant is strong in supportinginsertion loads and during use for supporting spinal compression loads.It is easy to fabricate and if the segments separate after insertion,spinal support would be largely unaffected.

A band saw presently available with a table guide is capable of holding0.0762 mm (0.003 inch) tolerances for fabricating such planks or in thealternative, a table saw can be used to cut planks from femoral rings.It is less desirable to cut strips from cortical strips or from longbone segments. Retaining pins preferably are friction fit attached asdescribed herein.

FIG. 47 illustrates an implant 584 comprising two planks 586 and 588 ofcortical bone pinned by two horizontal pins 590. This implant isrectangular on all sides. The joint between the planks is vertical wheninserted into the disc space. The pins and mating bores are as describedabove for the other embodiments.

In FIG. 48, implant 592 comprises a stack of vertically oriented planks594 preferably of the same thickness and which is not critical. Two pins596 connect the planks. The pins pass through all of the planks aspreferably occurs in all of the embodiments herein. The pins areattached by offsets or by different shapes and angles as discussedabove. The advantages of this implant are similar to those in regard tothe implant 564 of FIG. 46 and the disadvantages are as discussed withrespect to the implant of FIG. 44.

With respect to fiber orientation in the planks of the implants of thedifferent embodiments, it is preferred the orientation of the plank ofFIG. 48 be utilized when two pins are used to prevent spreading of anysplits which might occur and which splits do not adversely affect thecompression loading of the implant in this and related embodimentsutilizing vertically oriented planks as in implant 592.

The implant 596 of FIGS. 49-51 is made of one piece cortical bone. Ithas a posterior end 598 and an anterior end 600. In plan view in FIG.50, ends 598 and 600 are the same in cross sectional area and shape. Theimplant is of uniform thickness. It has two opposing sides 602 and 604which are mirror images of each other. It also has two opposing upperand lower vertebra engaging surfaces 606 and 608, respectively. Sides602 and 604 are convex and preferably elliptical. However, they may beformed as complex curves of multiple radii such as R1 and R2, FIG. 50.the surfaces 606 and 608 may be roughened or be grooved.

In FIG. 52, implant 610 has a square or rectangular posterior end 612and a square or rectangular anterior end 614. All surfaces taper andconverge toward end 612 forming a trapezoid shape from a normal view ofthat side. This implant is fabricated of one piece cortical bone or maycomprise stacked layers of planks as in the above embodiments.

In FIG. 53, implant 616 comprises a one piece cortical bone havingposterior end 618 and anterior end 620. Implant 616 has a top vertebraeengaging surface 622 and a bottom vertebrae engaging surface 624.Implant 616 appears the same as implant 596, FIG. 50 in top plan view.The sides 626 and 628 are convex curved in the form of a segment of anellipse or multiple radii of different values as in the embodiment ofFIG. 50. The difference between implant 596 and implant 616 is that thesurfaces 622 and 624 taper toward each other as seen in FIG. 54 so thatthe implant appears trapezoidal in side view. These shapes accommodatedifferent disc spaces that may be encountered during surgery.

In FIG. 66 an implant 630 comprises two planks 632 and 634 as discussedin connection with the FIG. 1 and certain of the related embodimentsabove. However, the implant 630 has a straight through bore 636 which isformed by axially aligned bores of the same diameter in each of theplanks 632 and 634. A curved pin 638 is forced into the bore 636. Thecurvature of the pin is such that the ends of the pin must bend intocoaxial alignment in order to be inserted in to the bore 636. Thisbending introduces compression and tension forces in the pin which istransferred into compression forces in the planks 632 and 634 directedin the plane of the planks. These forces hold and lock the planks to thepin. The fiber directions in the elements is as described for the otherembodiments.

In FIG. 75, implant 638 comprises two cortical bone planks 640 and 642.Two cortical bone pins 644, 645 are attached to mating bores normal tothe interfaces 646 and 647 of the planks. The pins may be as describedabove herein in connection with any of the embodiments of the pinarrangements but preferably employ the offset arrangement of FIG. 4. Theinterface surfaces 646 and 647 of the planks have a respectivecomplementary dovetail groove 648 and dovetail projection 649 formedtherein for mechanically locking the two planks together. The dovetailjoint extends in the longitudinal axial direction of the planks of axis650. The implant 638 is shown rectangular in overall shape but may beother shapes as described above for the other embodiments.

In FIG. 76, implant 651 comprises two planks 652 and 653 of corticalbone having a longitudinal axis 656 joined by two cortical bone pins654, 655 attached to mating bores normal to the interfaces 646 and 647of the planks. The pins may be as described above herein in connectionwith any of the embodiments of the pin arrangements, but preferablyemploy the offset arrangement of FIG. 4. The interface surfaces of theplanks have a respective complementary saw teeth and grooves 657 formechanically securing the two planks from relative displacement indirections 658. The teeth and grooves extend in the longitudinal axialdirection of the planks of axis 656. The implant 651 is shownrectangular in overall shape but may be other shapes as described abovefor the other embodiments.

In FIG. 77, implant 660 comprises two planks 661 and 662 of corticalbone having a longitudinal axis 664 joined by one cortical bone pin 665attached to mating bores normal to the plane of the interface surfacesof the planks lying in axis 664. The pin may be as described aboveherein in connection with any of the embodiments of the pinarrangements, but preferably employs the offset arrangement of FIG. 4.The interface surfaces of the planks have respective complementary sawteeth and grooves 666 for mechanically securing the two planks fromrelative displacement in directions 667 along the axis 664. The teethand grooves extend normal to the longitudinal axial direction of theplanks of axis 664. The implant 651 is shown rectangular in overallshape but may be other shapes as described above for the otherembodiments. The pin 665 has an offset or in the alternative, the matingbores in the two planks 661 and 662 are offset as shown in FIG. 4. Inthis embodiment, the direction of the offset of the bores 668 and 669,FIG. 77 a, (or of the pin sections) is in directions 667. In this waythe compression loads of the offset bent pin 665 are in the axialdirection of axis 664 and slippage of the planks 661 and 662 in thisdirection due to such compression loads induced by the bent pin isprecluded by the interengaged teeth and grooves 666. Similarly, a singlepin may be used in the embodiment of FIG. 76 in which the offset isdirected to impose relative slippage forces between the planks 652 and653 in the directions 658 which is resisted by the engaged teeth andgrooves 657.

In FIG. 78, an array of cortical bone planks 670, 671, 672, 673 and 674are shown in exploded view to show their stacked relation when joined.These planks have external dimensions that are preferably identical forpurposes of illustration, but need not be according to a givenimplementation. These planks are rectangular in plan view but also maybe other shapes as well. These planks are shown for purposes ofillustrating the relationship of offset bores in stacked planks forreceiving locking pins that are straight right circular cylinders ofcortical bone.

Plank 670 is identical to plank 672 and plank 671 is identical to plank673 in respect of the pin bores and their spaced relations. Plank 70 hastwo pin bores 674 and 676 which for purpose of illustration areidentical and are right circular cylinders lying on respective axes 678and 680. Plank 672 also has a set of bores 674 and 676 on respectiveaxes 678 and 680. Plank 671 is between planks 670 and 672 and has bores682 and 684 on respective axes 682′ and 684′. Axes 682′ and 684′ areoffset from respective axes 678 and 680 in opposing directions the sameamount. In this embodiment, the axes 682′ and 684′ are closer togetherthan axes 678 and 680 but in the alternative could be further apart.Similarly, plank 673 has a set of bores 682 and 684 on respective axes682′ and 684′.

Planks 670-673 are mounted together in abutting relation and may bebonded by an adhesive as described in the aforementioned U.S. Pat. No.5,899,939. The planks are mechanically joined by two identical pins suchas pin 243, FIG. 22, of appropriate length so that the ends of the pinare preferably flush with the outer exposed surface of planks 670 and673.

The two pins are bent by the offset of the bores in the planks 670-673is in opposing directions in any given corresponding plane parallel tothe plane of the planks. The pins thus exhibit multiple compression andtensile loads normal to the plane of the planks. These compressive andtensile loads translate into compression load components in the plane ofthe planks in opposite directions, frictionally locking the planks tothe pins. The pins are nominally the same diameter as the bores in theplanks so that only compressive loads in one direction is imposed oneach plank. This single compressive load direction minimizes thetendency of the planks to split along there fiber lengths as discussedin connection with FIGS. 80 and 82. The overall shape of the implant maybe further machined to the desired surface configuration for a givenimplementation.

In FIGS. 90-93, an implant 690 comprises two identical cortical bonepieces 692 and 694. These pieces interlock. Parts that have referencenumerals that are primed in piece 692 are identical to parts with thesame unprimed reference numeral in piece 694. Piece 694, FIGS. 92 and93, comprises a body 696, which may be square in plan view as seen inFIG. 93 or rectangular, from which a projection 698 extends. Theprojection 698 may also be square or rectangular in plan view.Thicknesses are exaggerated in the figures for purposes of illustration,the overall dimensions of the implant being in the ranges discussed inconnection with the embodiment FIG. 1.

Two like spaced projections 700 and 702 extend from a side 704 of body696. The projections 700 and 702 may be identical and extend from theside 704 the same distance 708 as the thickness 706′ of the projection698 (and thickness 706′ and 706 of the respective bodies 696′ and 696).The body 696 has the thickness 706 throughout. The spacing 710 betweenthe projections 700 and 702 is the same as the height dimension 712 ofthe projection 698.

The projections 700 and 702 straddle and receive therebetween theprojection 698′, FIG. 90. The projections 700′ and 702′ (not shown)straddle and receive therebetween the projection 698. The two pieces 692and 694 thus interlock and fit in close relation to form a solid blockof bone forming a solid rectangular polygon figure elongated indirections 714. This implant 690, FIG. 90, thus has the overallappearance of implant 638 (FIG. 75), implant 651 (FIG. 76), implant 660(FIG. 77), and the implants shown in FIGS. 47 and in FIGS. 62-67. Theseimplants may be further shaped as shown in the other embodiments to havetapering surfaces, ridges or saw teeth for gripping the engagedvertebra, chamfers for assisting in insertion and insertion toolcomplementary surface features, locking pins, interengaging saw teethand so on.

In FIG. 94 b, implant 716 is oval in overall plan view looking from thetop of the figure to the bottom. The implant 716 comprises two pieces718 and 720. Each piece has a planar interface surface 718′ and 720′respectively. The two pieces have a mating elements of a dovetail joint722 comprising a dovetail projection and a dovetail groove. The dovetailjoint interlocks the two pieces into a single implant structure similarto that described in FIG. 75. Offset pins (not shown) are optional. Itshould be understood that the term offset as applied to the pins meansthat either the pins are stepped and have axially offset portions as pin90 or the pins are not straight, such as the pins in FIGS. 23 and 31 forinsertion into a straight bore. Also the term offset as applied to thebores means the bores either are not straight, for receiving a straightpin or non-straight pin, or are stepped, as described above herein inFIG. 2 for example.

In FIG. 94 a, the pieces 718 and 720 are fabricated from a cortical bonering 724, the ring being formed as shown in connection with FIGS. 55 and56. the fiber direction is vertical running from the top to bottom ofthe drawing figure. The remaining sections 726 and 728 of the ring 724may be used to form planks, pins, screws and so on. A bone screw mayhave one or more helical threads. It should be understood that the shapeof the implant 716 shown is schematic and in practice its final shapewould conform to the desired shape and dimensions needed for insertionin a given spinal disc space or other insertion space.

In FIGS. 97-98, implant 730 comprises two mirror image identical pieces732, 732′. Pieces 732 and 732′ are fabricated from cortical bone ring734, FIG. 95. The two pieces are each semi-circular and formed from ahalf of circular cylindrical ring 734 which is machined to the exteriorshape. The central open core may also be machined by broaching forexample to form a central circular cylindrical opening in the medullarycanal of a long bone. Representative piece 732 has Identical slots 736and 738 formed in the body 740.

In the assembly, the slots 736 and 736′ of the two pieces areinterengaged. The slots 738 and 738′ of the two pieces are alsointerengaged at the same time. The resulting interlocked assembly isshown in FIGS. 97 and 98. The two pieces preferably are bonded togetherwith a suitable adhesive. The external surfaces may be tapered,chamfered and grooved according to a given implementation.

In respect of producing pins, the pins may be in interference fit oroffset. The pins are preferably formed from under utilized bone scrapleft over from plank manufacturing from larger bones using a hole orcore saw. Each pinned implant blank is machined to a finished implantincluding interface features for insertion tools. Conventional millingtechniques may be used to fabricate the various pieces of the differentembodiments. Surface features such as saw teeth or projections andgrooves are used to transmit loads and hold the pieces together asneeded.

In FIG. 99, implant 742 is shown by way of example for illustration as arectangular block of bone, but in practice may be of any shape orconfiguration, solid or hollow, as described hereinabove. The implant742 has two parallel pins 744 and 746 passing therethrough and extendbeyond opposite sides of the implant. The pins are secured in matingbores as described above. In the alternative, the pins 744 and 746 maycomprise four separate pins, for example, pin portions 744′ and 746′extending from side 745 of the implant, each pin extending from a blindbore (not shown) in the opposing sides 745, 745′ of the implant 742.

An implant insertion tool 748 includes a pair of mating spaced alignedtines 750, 752 on one side of the tool 748. Tines 750, 752 form a slot754 therebetween. The slot 754 is dimensioned to receive the protrudingpin portions of pins 744 and 746 in sliding close fit therewith.

The insertion tool 748 has a second pair of tines 756 and 758 whichdefine a slot 760 on a side of the tool opposite the tines 750 and 752.Slot 760 receives the pin portions 744′, 746′ of pins 744 and 746protruding from the opposite side of the implant 742. The tool 748 ofFIG. 100 shows the implant pins assembled to the tool slots 754 and 760.The tips 762 of the tines may be chamfered to facilitate insertion ofthe tool into the disc space of a patient's spine. The chamfers areinclined in opposite directions relative to each other on each pair 750,752 and 756, 758 to form a wedge shaped leading edge with the implant.The pins 744 and 746 may be of any of the shapes and configurations asdescribed above herein. The tool 748 and implant 742 with the protrudingpins helps keep the implant from twisting during insertion.

It will occur to one of ordinary skill that modifications may be made tothe disclosed embodiments without departing from the scope of theinvention as defined in the appended claims. The disclosed embodimentsare given by way of illustration and not limitation. For example, whilebone pins are preferred, pins of other known biocompatible materials maybe used for the implant planks. Also, the planks and implants may beformed of non-bone biocompatible materials.

1. A spinal fusion implant for fusing together two adjacent vertebracomprising: a first member having first and second opposing sides and afirst bore defining a central, longitudinal first axis, the first borebeing in communication with at least the first side; a second memberhaving third and fourth opposing sides and a second bore incommunication with at least the third side, the second bore defining asecond central longitudinal axis, the first and second axes forming afirst pair; and an elongated first pin located in the first and secondbores for securing the first member to the second member at theinterface formed by the facing first and third respective sides, the pinhaving a first section defining a third central longitudinal axis and asecond section defining a fourth central longitudinal axis, the thirdand fourth axes forming a second pair; one axis of at least one of thefirst and second pair of axes being offset relative to the other axis ofthe at least one pair of axes so as to place the pin in relativecompression and tension in the first and second bores for providing acompressive load on the surface of the first and second bores tofrictionally secure the members together; the first and second membersdefining a planar interface, further including an interengagingarrangement coupled to the first and second members adjacent to saidinterface for precluding translation displacement of the memberstransverse to said first and second axes in response to said compressionload on said surface of said bores the first member has a planarinterface surface at said first side, the second member having a planarinterface surface at the third side for abutting said first memberplanar surface in a plane, the first member defining an edge, the secondmember having a lea extending therefrom, the lea for abutment with theedge to form said interengaging arrangement to preclude relativetranslation of the first and second members in at least one direction insaid plane, said compression and tension creating compression forces insaid members in said at least one direction: each member being L-shapedwith the lea of each member forming a recess with its planar interfacesurface, each member having a portion adjacent to its lea in the recessof the other member. 2-14. (canceled)
 15. A spinal fusion implant forfusing together two adjacent vertebra comprising: a first member havingfirst and second opposing sides and a first bore defining a centrallongitudinal first axis, the first bore being in communication with atleast the first side; a second member having third and fourth opposingsides and a second bore in communication with at least the third side,the second bore defining a second central longitudinal axis, the firstand second axes forming a first pair; and an elongated first Din locatedin the first and second bores for securing the first member to thesecond member at the interface formed by the facing first and thirdrespective sides, the pin having a first section defining a thirdcentral longitudinal axis and a second section defining a fourth centrallongitudinal axis, the third and fourth axes forming a second pair; oneaxis of at least one of the first and second pair of axes being offsetrelative to the other axis of the at least one pair of axes so as toplace the Din in relative compression and tension in the first andsecond bores for providing a compressive load on the surface of thefirst and second bores to frictionally secure the members together;wherein the offset is formed by the at least one axis being non-parallelto said other axis.
 16. The implant of claim 15 wherein the one andother axes intersect.
 17. A spinal fusion implant for fusing togethertwo adjacent vertebra comprising: a first member having first and secondopposing sides and a first bore defining a central longitudinal firstaxis, the first bore being in communication with at least the firstside; a second member having third and fourth opposing sides and asecond bore in communication with at least the third side, the secondbore defining a second central longitudinal axis, the first and secondaxes forming a first pair; and an elongated first Din located in thefirst and second bores for securing the first member to the secondmember at the interface formed by the facing first and third respectivesides, the pin having a first section defining a third centrallongitudinal axis and a second section defining a fourth centrallongitudinal axis, the third and fourth axes forming a second pair; oneaxis of at least one of the first and second pair of axes being offsetrelative to the other axis of the at least one pair of axes so as toplace the pin in relative compression and tension in the first andsecond bores for providing a compressive load on the surface of thefirst and second bores to frictionally secure the members together;wherein the first and second sections are curved forming said secondpair of axes as a single continuous curved axis. 18-19. (canceled)
 20. Aspinal fusion implant for fusing together two adjacent vertebracomprising: a first member having first and second opposing sides and afirst bore defining a central longitudinal first axis, the first borebeing in communication with at least the first side; a second memberhaving third and fourth opposing sides and a second bore incommunication with at least the third side, the second bore defining asecond central longitudinal axis, the first and second axes forming afirst pair; and an elongated first Din located in the first and secondbores for securing the first member to the second member at theinterface formed by the facing first and third respective sides, the Dinhaving a first section defining a third central longitudinal axis and asecond section defining a fourth central longitudinal axis, the thirdand fourth axes forming a second pair; one axis of at least one of thefirst and second pair of axes being offset relative to the other axis ofthe at least one pair of axes so as to place the Din in relativecompression and tension in the first and second bores for providing acompressive load on the surface of the first and second bores tofrictionally secure the members together; wherein the first memberincludes a third bore and the second member includes a fourth bore incommunication with the third bore, and a further pin in the third andfourth bores, the first and second bores form a first elongated bore andthe third and fourth bores form a second elongated bore, said first andsecond elongated bores lying in spaced parallel planes, the projectionof the first and second elongated bores in a direction normal to saidplanes forming an X shaped image of said first and second elongatedbores in a plane parallel to said parallel planes. 21-23. (canceled) 24.A spinal fusion implant for fusing together two adjacent vertebracomprising: a first member having first and second opposing sides and afirst bore defining a central longitudinal first axis, the first borebeing in communication with at least the first side; a second memberhaving third and fourth opposing sides and a second bore incommunication with at least the third side, the second bore defining asecond central longitudinal axis, the first and second axes forming afirst pair; and an elongated first pin located in the first and secondbores for securing the first member to the second member at theinterface formed by the facing first and third respective sides, the Dinhaving a first section defining a third central longitudinal axis and asecond section defining a fourth central longitudinal axis, the thirdand fourth axes forming a second pair; one axis of at least one of thefirst and second pair of axes being offset relative to the other axis ofthe at least one pair of axes so as to place the Din in relativecompression and tension in the first and second bores for providing acompressive load on the surface of the first and second bores tofrictionally secure the members together; wherein the bores are inclinednon-perpendicular to the interface.
 25. A spinal fusion implant forfusing together two adjacent vertebra comprising: a first member havingfirst and second opposing sides and a first bore defining a centrallongitudinal first axis, the first bore being in communication with atleast the first side; a second member having third and fourth opposingsides and a second bore in communication with at least the third side,the second bore defining a second central longitudinal axis, the firstand second axes forming a first pair; and an elongated first Din locatedin the first and second bores for securing the first member to thesecond member at the interface formed by the facing first and thirdrespective sides, the pin having a first section defining a thirdcentral longitudinal axis and a second section defining a fourth centrallongitudinal axis, the third and fourth axes forming a second pair; oneaxis of at least one of the first and second pair of axes being offsetrelative to the other axis of the at least one pair of axes so as toplace the Din in relative compression and tension in the first andsecond bores for providing a compressive load on the surface of thefirst and second bores to frictionally secure the members together;including two sets of said first and second bores and a second pin, thefirst pin engaged with the first set of bores and the second pin engagedwith the second set of bores, wherein each set of bores are inclined atan angle not perpendicular to the plane of the interface of the members,the angle of one set of bores being oriented opposite to the orientationof the other set of bores. 26-30. (canceled)
 31. The implant of claim 25wherein the first and second axes of each set of bores are offset. 32.The implant of claim 25 wherein the third and fourth axes of therespective first and second sections of each pin are offset relative toeach other.
 33. (canceled)
 34. A spinal fusion implant for fusingtogether two adjacent vertebra comprising: a first member having firstand second opposing sides and a first bore defining a centrallongitudinal first axis, the first bore being in communication with atleast the first side; a second member having third and fourth opposingsides and a second bore in communication with at least the third side,the second bore defining a second central longitudinal axis, the firstand second axes forming a first pair; and an elongated first pin locatedin the first and second bores for securing the first member to thesecond member at the interface formed by the facing first and thirdrespective sides, the pin having a first section defining a thirdcentral longitudinal axis and a second section defining a fourth centrallongitudinal axis, the third and fourth axes forming a second pair; oneaxis of at least one of the first and second pair of axes being offsetrelative to the other axis of the at least one pair of axes so as toplace the pin in relative compression and tension in the first andsecond bores for providing a compressive load on the surface of thefirst and second bores to frictionally secure the members together;wherein the members each comprise sheet material, the sheet materialhaving opposing surfaces defining said sides, the members forming awedge having proximal and distal ends, the proximal end forming ananterior end and the distal end forming a posterior end, the implanthaving a longitudinal axis normal to the interface of said members andextending through said proximal and distal ends normal to the interfaceof said members, the elongated first pin extending along saidlongitudinal axis. 35-57. (canceled)
 58. A bone implant comprising:first and second cortical bone members each having a pin receiving boreat an interface therebetween; means for resisting translation of themembers relative to each other in a given direction; and a cortical bonepin in the bores for connecting the bone members; one of the pin andmating bores being offset relative to each other to create a compressiveand/or tensile force in the pin to create a static friction load to lockthe pin to the bone members in the given direction to thereby form thebone implant; the pin having first and second sections and at least onefirst outermost Peripheral surface defining a first transverse dimensiontherebetween at the first section defining a first central longitudinalaxis, the Din having at least one second outermost peripheral surfacedefining a second transverse dimension therebetween at the secondsection defining a second central longitudinal axis, the first andsecond axes forming a first pair of axes, the respective bores definingthird and fourth axes forming a second pair of axes; one axis of atleast one of the first and second pair of axes being offset relative tothe other axis of the at least one pair of axes so as to place the Dinin relative compression and tension in the first and second bores forproviding a compressive load on the surface of the first and secondbores to frictionally secure the members together.
 59. The implant ofclaim 58 wherein the bores are surfaced demineralized. 60-63. (canceled)64. A cortical bone implant comprising: a first cortical bone member; asecond cortical bone member abutting the first member, each memberhaving a pair of pin receiving bores; and a pair of first and secondDins, a different Din being in each member bore for attaching themembers to each other, the pins and bores being arranged to place thepins in both compression and tension, at least one of the bores havingfirst and second sections each defining a first transverse dimensiondefining a corresponding pair of first and second respective centrallongitudinal axes; one axis of one of the pair of first and second axesbeing offset relative to the other axis of the pair of axes so as toform a first offset arrangement of a given orientation and to place thefirst pin in relative compression and tension in the at least one borefor providing a compressive load on the surface of the at least one boreto frictionally secure the members together.
 65. The implant of claim 64wherein the implant extends in a longitudinal direction, the pins beingaxially spaced in the longitudinal direction.
 66. The implant of claim64 wherein the implant extends in a longitudinal direction, the pinsbeing spaced transversely relative to the longitudinal direction. 67.The implant of claim 66 wherein the second pin and its mating boresinclude a corresponding second offset arrangement having a givenorientation for creating said tension and compression, the offsetarrangement corresponding to one pin being oriented in an oppositedirection to the offset arrangement corresponding to the other pin. 68.The implant of claim 64 wherein each said pin of the pair of pins andmating bores includes an offset arrangement to cause each pin to exhibitcompression and tension wherein the direction of compression and tensionin one pin is in opposing mirror image directions to the other pin. 69.The implant of claim 64 wherein the bores of each mating pair eachdefine an axis and the bores of each pair are offset axially relative toeach other.
 70. The implant of claim 64 wherein the pins have first andsecond axially extending end sections, the end section of at least oneof said pins being offset axially from the other end section of that atleast one pin.
 71. A cortical bone implant comprising: a first corticalbone member; a second cortical bone member abutting the first member; athird cortical bone member, each member having a pin receiving bore; anda pin, the pin being in each member bore for attaching the members toeach other, the pin and bores being arranged to place the Din in bothcompression and tension; the pin being in said compression and tensionin at least two of said bone members, the compression and tension beingcreated by offset portions of a common bore.
 72. An implant comprising:a first planar member having two opposing broad surfaces having aperiphery defining a first plurality of edges; a second L-shaped memberhaving a first base member defined by a second plurality of edges and afirst leg extending from the base member at one base member edge forminga first recess, the first member being disposed in the first recess withan edge of the first member abutting the first leg, the edges of thefirst base member and the edges of the first member being coextensive;and a fastening arrangement for securing the first member to the secondmember; the first member being L-shaped including a second leg and asecond base member which forms a second recess, the first and secondbase members overlying each other with the first leg overlying an edgeof the second base member and the second leg overlying an edge of thefirst base member. 73-74. (canceled)
 75. An implant comprising: a firstL-shaped member having a first base portion and a first leg portion; asecond L-shaped member having a second base portion and second legportion; a third planar member disposed between the first and secondbase portions and between the first and second leg portions; and afastening arrangement for securing the me members together.
 76. Theimplant of claim 75 wherein the fastening arrangement for securingcomprises a pin in interference fit with a corresponding bore in atleast the first and second members.
 77. The implant of claim 76 whereinthe bores of the first and second members and the pin are arranged toplace the pin in both compression and tension to provide a compressiveload on the first and second members.
 78. The implant of claim 76wherein the first and second members are cortical bone.
 79. A spinalimplant comprising: a stacked plurality of planar cortical bone sheetseach with a bore, the implant having a length dimension in a givendirection, the sheets each having an abutting interface surfaceextending in the length direction with the corresponding bore at saidinterface; and a fastening arrangement including a pin extendingtransversely the length direction in said bores for securing the sheetstogether, the bores and pin being arranged so that the pin exhibitscompressive and tensile forces for applying a compressive load on atleast two of said sheets to hold the sheets together, a pair of thebores for receiving a Din being arranged offset relative to each otherfor creating said compressive and tensile forces on said Din.
 80. Aspinal implant comprising: a stacked plurality of planar cortical bonesheets, the implant having a length dimension in a given direction, thesheets each having an interface surface abutting an adjacent sheetextending transversely the length direction and a bore at the interfacesurface; and a cortical bone pin extending in the length direction insaid bores for securing the sheets together; the bores and Din beingarranged so that the pin exhibits compressive and tensile forces forapplying a compressive load on at least two of the sheets, one of (1)one section of the Din having an outer peripheral diameter that isoffset relative to a second Din section outer peripheral diameter and(2) the bores in at least two of said sheets being offset relative toeach other for creating said compressive and tensile forces. 81-87.(canceled)
 88. A method of forming a bone implant comprising: assemblingtwo cortical bone planks in parallel abutting relation; boring at leastone first bore in one of the bone planks in a first direction; andboring at least one second bore in the other of the bone planks in asecond direction generally opposite the first direction wherein thefirst and second bores are offset relative to each an amount such that astraight bone pin inserted in the bores is placed in compression andtension.
 89. The method of claim 88 wherein the bores have parallelaxes.
 90. The method of claim 88 wherein the offset of the axes is inthe range of about 0.1-10 mm.
 91. The method of claim 90 wherein theoffset comprises forming the first bore with its axis at an angle to theaxis of the second bore.
 92. The method of claim 90 wherein the firstand second bores are at a first angle relative to the planks, furtherincluding boring third bore in the first plank and a boring a fourthbore in the second plank at a second angle different than the firstangle.
 93. The method of claim 92 wherein the planks have an interfacedefining a plane, the method including boring the first and second boresat a first angle that is non-perpendicular with respect to the plane ofthe planks.
 94. The method of claim 93 wherein the third and fourthbores are bored at a second angle that is non-perpendicular with respectto the plane of the planks but in mirror image relation to the first andsecond bores.
 95. The method of claim 93 wherein the third and fourthbores are bored at a second angle normal to the plane of the planks. 96.A method of forming an implant comprising: forming first and secondcortical bone planks; forming a bore in each said planks; and insertinga bone pin in the bores so as to cause the pin to exhibit bothcompressive and tensile loads which compressively secure the planks tothe pin; the bores and Din being arranged so that the pin exhibitscompressive and tensile forces for applying a compressive load on thesheets, one of (1) one section of the Din having an outer peripheraldiametrical surface that is offset relative to a second Din sectionouter peripheral diametrical surface and (2) the bores in at least twoof said planks being offset relative to each other for creating saidcompressive and tensile forces.
 97. The method of claim 96 includingforming the pin from cortical bone exhibiting a fiber direction, the pinhaving a length dimension, the fiber extending in the length direction.98. The method of claim 96 including surface demineralizing the bores.99. The method of claim 96 including demineralizing at least the surfaceof said pin.
 100. The method of claim 96 including surface demineralizesaid bores and said pin.
 101. The method of claim 96 including fullydemineralizing at least a portion of the pin and surface demineralizingthe implant and said bores.
 102. A method of forming a bone implantcomprising: clamping a bone between first and second clamp members suchthat an end portion of the bone overhangs an end of the clamp members;and removing a portion of the overhanging end portion of the bone toform an implant plank.
 103. A method of forming an implant comprising:forming a plurality of implant members each defining a plane; abuttingthe members; and attaching a pin to the abutting members transverse tothe plane and creating opposing compressive forces against the membersby creating compressive and tensile bending loads in the pin to resistforces which otherwise tend to separate the members; the bores and Dinbeing arranged so that the pin exhibits compressive and tensile forcesfor applying a compressive load on the sheets, one of (1) one section ofthe Din having an outer peripheral diametrical surface that is offsetrelative to a second pin section outer peripheral diametrical surfaceand (2) the bores in at least two of said members being offset relativeto each other for creating said compressive and tensile forces.
 104. Themethod of claim 103 including forming the implant members of corticalbone.
 105. The method of claim 103 including forming the pin of corticalbone.
 106. The method of claim 103 wherein the step of attachingincludes bending the pin during the insertion of the pin into bores inthe members.
 107. The method of claim 103 wherein the step of formingthe implant members includes the step of forming the implant memberswith first and second offset bores and the step of attaching includesforming a straight cylindrical pin and forcing the pin into the offsetbores to bend the pin.
 108. The method of claim 103 wherein the step offorming the implant members includes forming first and second alignedbores of substantially the same transverse dimension in each member andthe step of attaching the pin includes forming the pin with offsetsections and then inserting the offset sections into said bores to bendthe pin.
 109. The method of claim 103 wherein the implant has loadbearing surfaces, the members comprising fibrous bone having a givenfiber direction, further including forming the implant with the bonefiber direction normal to the load bearing surfaces.
 110. A method offorming an implant comprising: forming first and second cortical bonemembers with a bore in each member; contracting a cortical bone pin bydehydrating the pin; inserting the dehydrated pin in the bore of eachmember; and then expanding the inserted pin to create an interferencefit between the pin and bone members in the bores.
 111. The method ofclaim 110 wherein the expanding step comprises immersing the insertedpin and attached bone members in a fluid solution.
 112. The method ofclaim 110 wherein the dehydrating contracting step includes placing thepin in a vacuum.
 113. The method of claim 110 wherein the expanding stepincludes hydrating the pin. 114-122. (canceled)
 123. A process forforming a bone implant comprising: forming a plurality of planks ofcortical bone, the planks having a broad surface terminating at edges,the surface being defined by a length and a width, the planks eachhaving a thickness; forming the broad surface of each of at least two ofsaid planks for mating in abutting relation; surface demineralizing allsurfaces of the at least two planks; clamping together the two at leastplanks with said mating broad surfaces abutting; washing the clamped atleast two planks; forming at least one bore in the at least two clampedplanks transversely the broad surfaces for receiving a locking pintherein; forming a locking pin and inserting the locking pin in said atleast one bore in each of the at least two clamped planks; forming aplurality of ridges on first and second opposing sides of said clampedplanks; surface demineralizing the formed ridges; freezing and/or dryingunder clamping pressure the resulting demineralized implant; and thenunclamping the implant.
 124. The process of claim 123 including formingsurface features in said broad mating surfaces.
 125. The process ofclaim 124 wherein said surface features include interlocking elementsfor locking the at least two planks from relative displacement in theplane of said mating surfaces in at least one direction.
 126. Theprocess of claim 123 including providing compression and tensile loadson said inserted pin to provide compression loads on the mating at leasttwo implants in at least one direction. 127-128. (canceled)
 129. Aprocess of making a spinal implant comprising: forming first and secondhydrated cortical bone planks with aligned bores; surface demineralizinga bone pin and then dehydrating the pin; inserting the dehydrated pininto the aligned bores; and then swelling the demineralized pin surfaceto provide a friction fit between the pin and bores.
 130. The process ofclaim 129 including surface demineralizing the bores.
 131. The processof claim 129 including forming the bores with the plank bone fibersnormal to the longitudinal axes of the bores. 132-138. (canceled)